This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Stoke Gifford Bypass Study
Policy Review & Scheme Appraisal
August 2006 JOB NUMBER: 5040208 DOCUMENT REF: StokeGifford_Report_v5.doc
v5 Final RCH SB SB 02/08/06
v4 Draft for issue RCH SB SB 18/05/06
v3 Third Draft RCH SB 28/04/06
v2 Second Draft RCH 04/04/06
v1 First Draft RCH 08/02/06
Originated Checked Reviewed Authorised Date
Revision Purpose Description
STOKE GIFFORD BYPASS STUDY Policy Review and Scheme Appraisal
5040208/Report/Final i StokeGifford_Report_v5.doc
Contents Section Page 1. Introduction 1.1
Background 1.1 Terms of Reference 1.2 This Report 1.3
2. Policy Review 2.1 Introduction 2.1 Objectives of the Stoke Gifford Bypass 2.3 Key Outcomes of the Stoke Gifford Bypass 2.3 Conclusions 2.16
3. Traffic Forecasting 3.1 BATS2 Model 3.1 Model Validation 3.2 Forecast Land-Use/Network Assumptions 3.7 Scheme Alternatives for Testing 3.9
4. Operational Assessment 4.1 Traffic Forecasts 4.1 Traffic Growth 4.1 Forecast Network Performance 4.1 Forecast Traffic Flows 4.2 Forecast Traffic Effects by Area 4.4 Changes in Bus Journey Times 4.5
5. Economic Appraisal 5.1 Construction Costs 5.1 Present Value Costs 5.2 Transport Economic Efficiency Benefits 5.3 TUBA Inputs 5.3 Economic Benefits of the Scheme 5.4 Accident Benefits 5.5 Summary of Accident Benefits 5.7 Summary of the Economic Appraisal 5.7
6. Conclusions 6.1
Appendix A 2016 Forecast Traffic Flows Appendix B 2016 Forecast Changes in Bus Journey Times
STOKE GIFFORD BYPASS STUDY Policy Review and Scheme Appraisal
5040208/Report/Final ii StokeGifford_Report_v5.doc
List of Figures Figure 2.1 – The Causal Chain Approach 2.2 Figure 3.1 – Location of Count Sites used for Model validation 3.6 Figure 3.2 – Alternative Options for Stoke Gifford Bypass 3.10 Figure 4.1 – Selected Links for Forecast Traffic Flows 4.10 Figure 4.2 – Forecast Traffic Effects of the Purple Route – 2016 AM Peak Hour 4.17 Figure 4.3 – Forecast Traffic Flows on the Purple Route – 2016 AM Peak Hour 4.18 Figure 4.4 – Bus Routes in GBBN Corridor 4 (Route 73) 4.19 Figure 5.1 – COBA Network 5.6
List of Tables Table 2.1 – National Policy Scheme Fit Matrix 2.4 Table 2.2 – Regional Policy Scheme Fit Matrix: Regional Transport Strategy 2.6 Table 2.3 – Regional Policy Scheme Fit Matrix: Funding Allocations 2.8 Table 2.4 – Sub Regional Policy Scheme Fit Matrix: Joint Replacement Structure Plan 2.10 Table 2.5 – Sub Regional Policy Scheme Fit Matrix: Greater Bristol Strategic Transport
Study 2.12 Table 2.6 – Sub Regional Policy Scheme Fit Matrix: Joint Local Transport Plan 2.14 Table 3.1 – Comparison of Modelled and Observed Flows – 2004 AM Peak Hour 3.4 Table 3.2 – Comparison of Modelled and Observed Flows – 2004 Inter-Peak 3.5 Table 3.3 – Summary of Scenario F Housing and Employment Forecasts 3.8 Table 4.1 – Forecast Network Performance – 2016 AM Peak Hour 4.6 Table 4.2 – Forecast Network Performance – 2016 Average Inter-peak Hour 4.7 Table 4.3 – Forecast Network Performance – 2031 AM Peak Hour 4.8 Table 4.4 – Forecast Network Performance – 2031 Average Inter-peak Hour 4.9 Table 4.5 – Forecast Traffic Flows – 2016 AM Peak Hour 4.11 Table 4.6 – Forecast Traffic Flows – 2016 Inter-peak Hour 4.12 Table 4.7 – Forecast Traffic Flows – 2031 AM Peak Hour 4.14 Table 4.8 – Forecast Traffic Flows – 2031 Inter-peak Hour 4.16 Table 5.1 – Scheme Costs 5.2 Table 5.2 – Economic Efficiency Benefits of the Stoke Gifford Bypass 5.4 Table 5.3 – Summary of Forecast Accident Benefits 5.7 Table 5.4 – Economic Appraisal of the Stoke Gifford Bypass Scheme 5.9
STOKE GIFFORD BYPASS STUDY Policy Review and Scheme Appraisal
1. Introduction 1.1 In November 2005, Atkins Planning Consultants were commissioned by
South Gloucestershire Council (SGC) to undertake a review of the proposed Stoke Gifford Bypass, which would provide a link between Great Stoke Way (at its southern end) and the A4174 Avon Ring Road. This review was to be independent and impartial.
1.2 This report presents the findings of the Atkins study, including a policy review and an operational and economic appraisal of scheme options.
BACKGROUND Winterbourne Bypass
1.3 The Winterbourne bypass was first proposed in the mid-1980s to provide a strategic route between Yate and Bristol, which would bypass Winterbourne/ Frampton Cotterell, and improve access to the county and motorway network.
1.4 A proposal for the bypass was included in the Avon County Structure Plan of 1994, and assessed as part of the Avon North West Sector Study undertaken by MVA. This study recommended the full scheme on balance, but showed that the economic case for the southern section of the proposed route (from the B4057 to the Avon Ring Road at Harry Stoke) was stronger than that for the northern section (from Iron Acton to the B4057 Winterbourne Road). Subsequent work by Oscar Faber in 1997 confirmed the relative merits of the southern section. It was therefore promoted as a key element of the Bristol North Fringe Multi Modal Project for SGC’s TPP submission of 1997/98.
1.5 However, following further work by Steer Davies Gleave for LTP1 and the Public Examination of the Deposit Structure Plan, the by-pass was excluded from the revised Structure Plan of February 2000. It was formally abandoned by SGC in May 2000.
1.6 More recently, a full Winterbourne Bypass proposal has been re-examined by the Greater Bristol Strategic Transport Study. An economic appraisal of the scheme, based on a single 2031 AM peak hour assignment and limited to weekday peak period benefits only, showed that it would generate very significant user benefits and return a Benefit/Cost Ratio (BCR) of 8.3 over 60 years. Most of the user benefits would be travel time savings resulting from relief of congestion in the North Fringe area.
Stoke Gifford Bypass 1.7 The most southerly section of the Winterbourne bypass, formerly known as
the ‘Bradley Stoke Link’ or ‘Winterbourne Bypass Southern Section’ was originally intended to provide a connection between the southern end of Bradley Stoke Way and the A4174 Avon Ring Road. A first section of the bypass (now known as Great Stoke Way) was constructed and opened several years ago. It was constructed to dual carriageway standard between the B4057 Winterbourne Road and the roundabout junction with Hunts Ground Road.
1.8 The current proposal would complete the link between Great Stoke Way and the A4174 Avon Ring Road, traversing the main railway line and bypassing Stoke Gifford on its east side. It would also need to bypass new housing in
STOKE GIFFORD BYPASS STUDY Policy Review and Scheme Appraisal
the Hunts Ground area, which has been developed on land formerly safeguarded for the proposed route.
1.9 The main aim of the bypass would be to provide traffic relief to the road network in Stoke Gifford, which already suffers significant congestion during peak periods, particularly on Winterbourne Road, Hatchet Road, Brierley Furlong and Great Stoke Way. It would also accommodate further traffic growth generated by proposed developments at Harry Stoke and elsewhere in the North Fringe area.
TERMS OF REFERENCE 1.10 The aims and objectives of the study, its requirements, scope of work and key
deliverables were set out in the Consultant’s brief of October 2005. These were discussed and clarified at a meeting with Officers and Elected Members of the Council on 19 October 2005.
1.11 The Atkins proposal letter of 2 November 2005 defined our approach to the study, based on our understanding of its requirements. The main aims of the study were outlined as follows:
♦ To assess the benefits and implications of a new link road in Stoke Gifford, between Great Stoke Way and the A4174 Avon Ring Road. A key aim of this road would be to provide relief to Stoke Gifford from existing congestion and future developments;
♦ To carry out an appropriate assessment of alternatives (including bus only);
♦ To consider implications on the highway network and propose, where necessary, a package of complementary measures to ensure traffic uses an appropriate route, that road safety is improved and that use of sustainable modes (cycling, walking and public transport) is encouraged;
♦ To carry out a brief policy review to determine how the bypass fits with local and regional policies;
♦ To carry out a desktop review of major engineering issues; and
♦ To consider the deliverability of the scheme and funding sources.
1.12 It was understood from the outset that officers of SGC would undertake an environmental assessment of the scheme, and that this would not form part of the Atkins brief.
1.13 The SGC scope of work was subsequently extended to include the desktop review of engineering issues, identification of scheme alternatives and estimation of preliminary construction costs for scheme appraisal.
1.14 It was agreed at the meeting of 19 October 2005 that traffic forecasts for 2016 and 2031 would be produced using the Bristol Area Transport Study model (BATS2), which was updated to appraise the JLTP Greater Bristol Bus Network Major Scheme Business Case of July 2005. Officers and Elected Members also accepted that study time constraints and the preliminary nature of the assessments required at this stage would not allow for a major recalibration and revalidation of the BATS2 model.
STOKE GIFFORD BYPASS STUDY Policy Review and Scheme Appraisal
THIS REPORT 1.15 This report presents the results of the traffic modelling and economic analysis
of the scheme. It includes an assessment of how the scheme ‘fits’ with current local, regional and national transport policy followed by a detailed traffic analysis of scheme impacts on the local highway network.
1.16 The report concludes on whether the scheme should be considered for implementation to address local traffic, transportation and environmental considerations.
STOKE GIFFORD BYPASS STUDY Policy Review and Scheme Appraisal
2.1 The likely cost of a Stoke Gifford Bypass would be well beyond the financial means of South Gloucestershire Council and its partners. The only realistic method of funding the scheme would be a combination of developer contributions and Department for Transport (DfT) Major Scheme funding.
2.2 The DfT guidance places heavy emphasis on a major scheme being fully consistent with local, regional and national policies.
2.3 Paragraphs 2.16 and 2.17 of the “Guidance to Local Authorities Seeking DfT Funding for Transport Major Schemes” states:
The Strategic Case is essentially the “fit” of the scheme in terms of wider objectives. We expect major scheme bids to be for those schemes that will enhance the objectives of the LTP or the wider objectives of the authority, such as regeneration and social inclusion. Major scheme bids should be explicit about how they would help to deliver LTP targets and to what extent targets could be stretched were the scheme to be funded. Where the benefits of a scheme would only be realised after the second LTP period, bids should make reference to the potential of the scheme to meet the longer term objectives of the authority.
The Strategic case will also need to show the fit with the strategies of regional authorities, notably the Regional Transport Strategy/Regional Spatial Strategy, within which the LTP sits. Where appropriate, the Strategic Case should also describe the fit with other transport delivery agencies' plans and objectives.
2.4 The concept of scheme “fit” is not simply about judging whether a scheme is broadly consistent with policy objectives. Rather it is about a scheme making an active contribution to delivering particular objectives. This can be explained by the concept of the causal chain (see Figure 2.1).
2.5 The causal chain approach shows how the inputs, outputs and outcomes the Stoke Gifford Bypass scheme should progress in a logical order so that the various local, regional and national objectives / targets are met.
2.6 The most important part of the causal chain is the link between the scheme outputs (in this case the new highway infrastructure) and the desired outcomes (reduced congestion on local roads and better quality public transport services that are well patronised). If the desired outcomes do not result from the inputs / outputs then the fit of the scheme with objectives will be seriously compromised.
STOKE GIFFORD BYPASS STUDY Policy Review and Scheme Appraisal
Inputs (policy framework, capital / revenue investment and staff resources that are
invested in planning and constructing the Stoke Gifford Bypass)
Outputs (the highway and associated bus priority infrastructure delivered by the Stoke
Gifford Bypass)
Outcomes (the impact on travel behaviour and travel conditions resulting from delivery of
the highway infrastructure)
Objectives (the wider local, regional and national aims - towards which the outputs and
outcomes contribute)
Performance Indicators and Targets (a quantifiable measure showing how outputs / outcomes deliver objectives)
2.7 We have therefore undertaken a comprehensive review of the outputs and outcomes of the Stoke Gifford Bypass in order to judge their likely contribution to the following policy and strategy documents:
♦ DfT White Paper The Future of Transport: A Network for 2030.
♦ Regional Planning Guidance 10 and the replacement Regional Spatial Strategy (including the Regional Transport Strategy).
♦ GOSW Regional Funding Allocations Paper.
♦ South Gloucestershire Local Plan.
♦ Greater Bristol Strategic Transport Study.
♦ South Gloucestershire Local Transport Plan.
♦ South Gloucestershire Road Traffic Reduction Act Report.
♦ Greater Bristol Joint Local Transport Plan.
2.8 In order to assess the fit of the scheme with the above documents we have devised a five point scale:
4: scheme demonstrably contributes to delivery of all the policy objectives. 3: scheme is broadly consistent with most or all of the policy objectives. 2: scheme is broadly consistent with a few of the policy objectives. 1: scheme has no obvious effect on the policy objectives. 0: scheme is contrary to some or all of the policy objectives.
2.9 For each policy document we have assessed the fit between the objectives, outputs and outcomes of the Stoke Gifford Bypass scheme with the various
STOKE GIFFORD BYPASS STUDY Policy Review and Scheme Appraisal
national, regional and local policy / strategy documents. Depending on the available evidence we have then allocated a score between 0 and 4 for:
♦ Fit between each scheme objective and the related policy document objective.
♦ Fit between each scheme output / outcome and the related policy document objectives.
2.10 The score for each objective and output / outcome will be averaged to provide an overall score between 0 and 4 for the policy fit. The two average scores will then be added together. Therefore for each of the eight policy documents we have reviewed, the Stoke Gifford Bypass could score a minimum of 0 and a maximum of 8 points.
2.11 There is a crucial distinction between the two parts of the scoring process. It is relatively easy to demonstrate a fit between scheme objectives and wider policy objectives. However it is much more challenging for a scheme to actively demonstrate a good fit with the actual or predicted outputs and outcomes (which may or may not deliver the scheme objectives) and the wider policy objectives.
2.12 The purpose of the scoring is not to provide a definitive view on whether this particular scheme - if submitted as a major scheme bid - will meet the requirements of the DfT guidance. Rather it is an attempt to outline how the scheme, as it is currently defined, fits with current local, regional and national policy as a means of identifying strengths and weaknesses that promoters will need to develop and address.
OBJECTIVES OF THE STOKE GIFFORD BYPASS 2.13 The consultant brief issued by South Gloucestershire Council lists a number
of objectives for the Stoke Gifford Bypass:
♦ Provide relief to Stoke Gifford from the current heavy traffic and that associated with future developments.
♦ Ensure (through a range of complementary measures) that traffic follows the appropriate route.
♦ Improve road safety.
♦ Encouragement of sustainable modes including cycling, walking and public transport.
KEY OUTCOMES OF THE STOKE GIFFORD BYPASS 2.14 Tables 2.1 to 2.5 present a summary of how the proposed bypass ‘fits’ with
policy. It includes an assessment of the scheme infrastructure and the traffic impacts, details of which are included in Section 4.
STOKE GIFFORD BYPASS STUDY Policy Review and Scheme Appraisal
Table 2.1 – National Policy Scheme Fit Matrix DfT White Paper The Future of Transport: A Network for 2030. National Policy Objective / Theme Stoke Gifford Bypass
Scheme Objectives Stoke Gifford Bypass Scheme Outputs and Outcomes
Road network to provide a more reliable and freer flowing service for personal travel and freight, with people making informed choices about how and when they travel. Road capacity to be provided where it is needed (and when environmental and social costs are justified). Benefits of new investment should be “locked in” through measures such as car pool lanes and road tolling.
A key objective is to reduce congestion locally in Stoke Gifford. There is also recognition of the potential wider impact of the bypass. However there no obvious link to the issue about allowing people to make informed choices. Environmental and social benefits are not explicitly stated as objectives but could be assumed to result from traffic relief. There is some recognition in the scheme objectives of locking in the capacity provided (via unspecified traffic management measures) Score: 3
The bypass provides traffic relief to the centre of Stoke Gifford, reducing the considerable impact of traffic congestion. The provision of additional local highway capacity also improves journey reliability and results in a more free-flowing network, reflected in the reduction in overall journey time and delay within the traffic model. This effect is however local to the scheme, and in some instances additional traffic is attracted to other routes as traffic takes advantage of the routing opportunities created by the scheme. Score: 2
The rail network providing a fast reliable and efficient service, particularly for inter urban journeys and commuting into large urban areas.
The scheme does have access to Bristol Parkway station as a key part of the wider objective for traffic relief in the Stoke Gifford area. Score: 3
The scheme provides improved access to Bristol Parkway from the south east (via the Ring Road and M32). The reduction of traffic and congestion in Stoke Gifford will also result in better traffic conditions and improved journey reliability for traffic and buses approaching the station from the south west and the north. Score: 4
Bus services that are reliable, flexible, convenient and tailored to local needs.
The scheme does aim to mitigate the effects of congestion on local bus services and will provide opportunities for greater bus priority. Score: 4
The relief of congestion through Stoke Gifford will reduce the impact traffic congestion has on bus services through the village. This bus corridor, via Hatchet Road and Brierley Furlong, is included in the Greater Bristol Bus Network. Opportunities for bus priority in the Stoke Gifford section of this corridor are significantly constrained by the Bristol Parkway railway bridge and by residential development in Stoke Gifford itself. Therefore the reduction in traffic and congestion on this route will
STOKE GIFFORD BYPASS STUDY Policy Review and Scheme Appraisal
directly benefit buses, which will in turn increase their attractiveness as an alternative travel mode. Score: 4
Making walking and cycling a real alternative for local trips.
This is a key objective of the scheme although the detail of how this will be delivered is less clear. Score: 3
The reduction of traffic in Stoke Gifford will benefit pedestrians and cyclists, by improving the environment in terms of pollution, noise and visual intrusion. The bypass will also include a cycle track as a component of its design, so a new cycle route will be provided between the east of Stoke Gifford and Bradley Stoke and the Harry Stoke development, UWE and destinations to the east via the Ring Road Cycle track: Score: 4
Ports and airports providing improved international and domestic links.
No obvious direct link to this objective except as part of a wider strategy for improving access to the docks and Bristol Airport. Score: 2
The scheme has very local impacts, so it is difficult to link the bypass to benefits at ports and airports. However the provision of link between the M32 and the eastern access to Parkway Station may enable consideration of a Bristol Airport bus service to operate additionally from Bristol Parkway. Score: 2
Overall Assessment and Score The scheme objectives as currently defined are broadly consistent with national policy objectives although more detail would be required for submission as part of a major scheme bid Score: 3
The scheme broadly delivers the national policy objectives, but it is noted that its impacts are generally local, benefiting local travel patterns to Stoke Gifford and Bradley Stoke. Score: 3
STOKE GIFFORD BYPASS STUDY Policy Review and Scheme Appraisal
Table 2.2 – Regional Policy Scheme Fit Matrix: Regional Transport Strategy Regional Spatial Strategy Regional Policy Objective Stoke Gifford Bypass
Scheme Objectives Stoke Gifford Bypass Scheme Outputs and Outcomes
• Transport and the Strategically Significant Cities and Towns (SSCTs)
One of the scheme objectives does make reference to heavy traffic associated with future developments and its location in the largest SSCT in the south west demonstrates good synergy with RTS priorities. However the RTS places even greater emphasis on improving non car modes (which is covered by the study objectives) and demand management (which is not). Also the bypass is essentially local in nature and it is questionable whether it is a regionally significant scheme on its own. Score 3
The bypass supports the regional strategy by reducing traffic congestion in the north of the Greater Bristol SSCT and enabling improved access to services and facilities. This is shown by the reduction in traffic congestion in Stoke Gifford and in the area around Abbey Wood. However the impact of any demand management measures in the area has not been explicitly modelled and the wider impact of the scheme is not the primary source of the benefits. Score: 3
• Providing reliable connections to the UK, European and International markets.
There is no specific scheme objective related to impact on the strategic road network although this issue was looked at by GBSTS. Score 2
There is some evidence from GBSTS and this more recent work that there is a degree of traffic reduction benefit to the M4 / M5. Score 3
Ports and airports No obvious direct link to this objective except as part of a wider strategy for improving access to the docks and Bristol Airport. Score: 2
The scheme has very local impacts, so it is difficult to link the bypass to benefits at ports and airports. However the provision of link between the M32 and the eastern access to Parkway Station may enable consideration of a Bristol Airport bus service to operate additionally from Bristol Parkway. Score: 2
• Setting parking standards through accessibility planning
The study is not relevant to this issue. Score 1 The study is not relevant to this issue. Score 1
Regional Connectivity and Freight Transport There is no objective relating to regional connectivity although it could be argued that as the north of Bristol is a significant generator and attractor of freight traffic then the scheme will provide some benefit at one end of a longer journey. Score 2
The congestion benefits of the Stoke Gifford bypass will result in a reduction in journey time and greater journey time reliability for freight movements that have an origin / destination in the Bradley Stoke area. Score 2
STOKE GIFFORD BYPASS STUDY Policy Review and Scheme Appraisal
Overall Assessment and Score The scheme objectives as currently defined are
partly consistent with the majority of regional policy objectives although more detail would be required for submission as part of a major scheme bid. As a free standing proposal the scheme does not have regional traffic movements as its primary objective. Score: 2
Although a local scheme with generally local impacts, the traffic analysis of the bypass shows that it is broadly consistent with most of the regional policy issues listed here. Score: 2
STOKE GIFFORD BYPASS STUDY Policy Review and Scheme Appraisal
Table 2.3 – Regional Policy Scheme Fit Matrix: Funding Allocations Regional Funding Allocations: Advice from the South West Region Regional Policy Priorities for Investment Stoke Gifford Bypass
Scheme Objectives Stoke Gifford Bypass Scheme Outputs and Outcomes
Promoting more sustainable patterns of transport The scheme does not have an explicit objective of promoting more sustainable patterns of development but instead seeks to address problems that have arguably been the result of unsustainable development in the past. However this is not to say that the scheme cannot be part of an integrated package of measures that could assist with promoting more sustainable travel patterns in the area. Score 2
The scheme does not directly support sustainable travel, but the cycle track alongside the bypass will be a new piece of cycle infrastructure and the relief of congestion in Stoke Gifford will directly benefit bus services in this corridor, which also forms a component of the GBBN. Score: 3
Supporting development and economic activity in the strategically significant towns and cities through improved public transport, demand management and selectively providing for new roads
The scheme could well fall into the category of being a “selective” new road if it can be demonstrated that there is no serious alternative to addressing the traffic problems in the Stoke Gifford area. Score 3
The bypass does demonstrate a benefit to the residents of Stoke Gifford, and is the only realistic alternative given the significant constraint of the railway line and development between Stoke Gifford and the Ring Road. Score: 3
Improving the reliability and resilience of inter and intra regional connectivity as a strategic route into the region, on regionally significant transport corridors and on other transport corridors
The scheme is not on the strategic road network but could make a contribution to making better use of the existing motorway network if it could be demonstrated that it caters for trips that would otherwise use the M4 / M5. Score 2
The scheme is very local in impact, but some relief to the M4 is shown between Junctions 19 and 20 as the bypass provides an alternative route between Bristol, the M32 and the Aztec West/Almondsbury Business Park areas. Score: 2
Tackling access to jobs and delivery of services in rural areas
There is no obvious benefit to any rural areas as a result of this scheme. Score 1
The scheme generally does not provide a significant benefit to rural areas, serving primarily an urban area and a suburban hinterland (between Stoke Gifford and Yate). Score: 1
Delivering against DfT / regional “shared priorities”
The scheme does have explicit objectives related to two of the four DfT / LGA shared priorities – congestion and safety. There is no explicit recognition of accessibility or air quality in the
The scheme does provide significant network-wide decongestion benefits, although accidents are shown to increase slightly overall because of changes in the length of some journeys. However
STOKE GIFFORD BYPASS STUDY Policy Review and Scheme Appraisal
scheme objectives – although these could be inferred. Score 3
the reduction of traffic in Stoke Gifford centre, where pedestrian and cyclist activity may be expected, will make this area safer. The bypass also improves accessibility to Bristol Parkway and provides a new cycle link. Score: 3
Overall Assessment and Score The scheme fits slightly less well against a broader range of regional objectives mainly because it does not make any contribution to rural issues. However this lower score should be seen in the context that few, if any, schemes are going to perform equally well against rural and urban objectives. Score 2
The bypass scheme does have largely local benefits, and the score against the rural objective is understandably weak. Hence its score against these regional objectives is lower when compared to its ‘fit’ against other objectives. Score: 2
STOKE GIFFORD BYPASS STUDY Policy Review and Scheme Appraisal
Table 2.4 – Sub Regional Policy Scheme Fit Matrix: Joint Replacement Structure Plan Joint Replacement Structure Plan Policy 58 Proposals for alterations to the non-trunk road network will be assessed and advanced only where: Local Policy Objective / Theme Stoke Gifford Bypass
Scheme Objectives Stoke Gifford Bypass Scheme Outputs and Outcomes
(i) the improved access will assist urban regeneration or address problems from planned development or
The scheme has development related traffic problems as an explicit objective. Score 4
The scheme is shown to directly address and alleviate development-related traffic problems. Score: 4
(ii) they are necessary for the solution of a severe road safety or environmental problem; and
The scheme has an explicit objective to improve road safety and an implicit objective to improve the environment through traffic relief in built up areas in the north of Bristol. Score 3
The scheme is shown to directly address and alleviate development-related congestion, relieving Stoke Gifford and hence improving its environment. It will also improve safety locally in Stoke Gifford, although overall the effects of the scheme across a wider area suggests a slight increase in the number of accidents as a consequence of the scheme Score: 3
(iii) the potential for benefits to safety, the environment and public transport operations are clear; and
The scheme should improve safety by removing traffic from roads that are not able to cope with the large volumes now present – so that in theory the potential for conflict between motor vehicles should be reduced. Furthermore the removal of traffic from built up areas should help to reduce potential for collisions between motor vehicles and vulnerable road users. The scheme should deliver improvements to public transport operations through reducing general congestion and allowing implementation of greater levels of bus priority. Score 4
The scheme delivers against all of the multi modal scheme objectives by ensuring that traffic is removed from local roads and space is reallocated to walking, cycling and public transport. Score: 4
STOKE GIFFORD BYPASS STUDY Policy Review and Scheme Appraisal
(iv) no reduction is likely in existing, or future, public transport usage; and
On its own the scheme cannot deliver this objective but can make a contribution by allowing public transport journeys to become faster and more reliable. Score 2
The scheme will provide a benefit to buses locally by reducing traffic flows, delays and journey time variability and hence improving service reliability in one of the key GBBN corridors. This is important as opportunities for further bus priority improvements in the Stoke Gifford area are severely constrained by the railway bridge at Bristol Parkway station. Hence the scheme will benefit bus services and their passengers. Score: 3
(v) all alternatives giving priority to other modes than the car have been considered; and
The scheme objectives make it clear that alternative modes such as cycling, walking and public transport will be encouraged. Score 4
The scheme has been developed having considered all other options in numerous traffic studies, including the Avon Ring Road and GBBN Major Scheme Bids. It has also been deleted from the Council’s policies in the recent past; its reconsideration now is a consequence of considering all other options. Score: 4
(vi) no significant reduction in journey time will result from car traffic along a main road corridor used for commuting; and
By its nature the scheme is going to allow traffic that uses the bypass to reduce its journey time compared with the current heavily congested route. The challenge is to ensure that the roads bypassed do not experience large increases in journey time for traffic that should be using an alternative route. The scheme has an explicit objective to use traffic management measures to ensure that traffic follows the appropriate route. Score 3
The scheme does provide congestion relief and hence journey times for all traffic will be reduced. However, although the reduction in journey time is measurable, it is not significant and hence will not result in a marked increase in commuting by car. Score: 3
(vii) facilities for pedestrians and cyclists are retained or enhanced.
The scheme objectives make it clear that alternative modes such as cycling, walking and public transport will be encouraged. The removal of traffic from residential roads will allow pedestrian and cycle priority schemes to be delivered. Score 4
The scheme includes a cycle track within its planned infrastructure, and the relief to Stoke Gifford will improve conditions for pedestrians and cyclists. Score: 4
Overall Assessment and Score Overall there is a good fit between the scheme objectives and the Structure Plan Policy 58. Score 3
The scheme strongly supports the policy objectives detailed in this matrix. Score: 4
STOKE GIFFORD BYPASS STUDY Policy Review and Scheme Appraisal
Table 2.5 – Sub Regional Policy Scheme Fit Matrix: Greater Bristol Strategic Transport Study
Greater Bristol Strategic Transport Study Local Policy Objective / Theme Stoke Gifford Bypass
Scheme Objectives Stoke Gifford Bypass Scheme Outputs and Outcomes
Develop a series of integrated, multi-modal transport strategies over time for the study area identifying, analysing and appraising solutions to problems on the national strategic transport networks, on the local strategic transport networks and at the interface between them, so as to improve strategic transport movements into, out of and through the study area
There is no specific reference to strategic traffic movements or networks in the study objectives with relief to Stoke Gifford being the primary objective. However this is not to say that local traffic relief could not also have a benefit to the strategic network. Score 2
GBSTS model results show that if the Winterbourne Bypass was connected to the A4174 ARR with traffic crossing the M4 via the B4427 Old Gloucester Road, the scheme would provide some relief to the M4 and M5. Our more recent work on the Stoke Gifford bypass is consistent with the findings of GBSTS. Score 2
Develop transport strategies that support existing economic activity, continue sustainable development and assist economic regeneration of urban areas and the wider process of urban renewal within the study area
The study objective of providing traffic relief to Stoke Gifford is broadly consistent with the aim of supporting sustainable economic regeneration and development although much depends on the ability to limit future traffic growth and boost patronage of non car modes. Score 3
The GBSTS model concludes that there is a measurable congestion reduction benefit and as a result this will help to assist the attractiveness of the area for inward investment and regeneration. The work we have undertaken on the Stoke Gifford bypass is clearer on what the sustainability benefits will be – in particular positive impacts on public transport as a result of congestion relief. Score 3
Reduce the impact of transport on the environment
The scheme does aim to enhance the built environment by removing traffic and associated congestion from residential areas of north Bristol. Again there is recognition of the need to encourage sustainable travel modes. The main concern is that the additional highway capacity should not result in a significant increase in demand for car travel. Score 3
The bypass does reduce traffic volumes in the centre of Stoke Gifford, which is the aim of the bypass. However it also results in the redistribution of some traffic with a consequential increase in traffic on some other roads, notably on the southern section of Bradley Stoke Way and on Winterbourne High Street and Beacon Lane. On balance it is considered that the bypass provides a greater environmental benefit than it does a disbenefit, and enables local bus service to operate more efficiently. Score: 3
STOKE GIFFORD BYPASS STUDY Policy Review and Scheme Appraisal
Overall Assessment and Score The main difference between GBSTS and the Stoke Gifford Bypass study is that the latter is primarily concerned with traffic relief of a local area and any benefits to the strategic road network will only come about if the bypass removes local traffic currently using the M4 and M5. If this geographical dimension is put to one side then the objectives of GBSTS and the Stoke Gifford bypass are in many ways fairly similar. Score 3
The modelling work between GBSTS and the Stoke Gifford bypass study does show broadly consistent results even though the latter is a more focussed study of a local area. Score 3
Table 2.6 – Sub Regional Policy Scheme Fit Matrix: Joint Local Transport Plan Greater Bristol Joint Local Transport Plan Local Policy Objective / Theme Stoke Gifford Bypass
Scheme Objectives Stoke Gifford Bypass Scheme Outputs and Outcomes
To tackle congestion: • promote use of alternatives to the private car • encourage more sustainable patterns of
travel behaviour • manage the demand for travel by the private
car
Congestion relief is a key reason for consideration of the scheme. However this appears to be primarily because of the removal of traffic from a road that is unable to cope with current and future volumes and the provision of a new alignment with enhanced capacity. The extent to which the scheme could deliver a significant increase in use of alternative modes (as opposed to mere “encouragement”) is not clear. There is a potential danger that additional road capacity could, in the absence of suitable demand management measures, could lead to increased demand for car travel. Score 2
The traffic forecasts show relief to Stoke Gifford village centre. However, because of the generally congested nature of the highway network in the North Fringe, the effect of the scheme locally would appear to have a redistribution effect and flows on routes post-implementation are not of an order of magnitude that is likely to significantly encourage increased use of single-occupant vehicles for commuting; the Ring Road corridor remains congested and rat-running can also be detected. At the same time, there is a measurable reduction in journey times on the parallel routes through Stoke Gifford and these will benefit bus services in this corridor. Score: 3
To improve road safety for all road users: • ensure significant reductions in the number
of the most serious road casualties • achieve improvements for road safety for the
most vulnerable sections of the community
Safety is a key objective of the scheme. The scheme should improve safety by removing traffic from roads that are not able to cope with the large volumes now present – so that in theory the potential for conflict between motor vehicles should be reduced. Furthermore the removal of traffic from built up areas should help to reduce potential for collisions between motor vehicles and vulnerable road users. Score 4
The traffic model overall does suggest a slight network-wide increase in accidents as a result of the scheme. However the reduction of traffic flows through Stoke Gifford will reduce the incidence and severity of accidents in this corridor. Score: 3
To improve air quality: • improve air quality in the Air Quality
Management Areas
The scheme is not in a designated AQMA and has no specific air quality improvement objective. Nevertheless the removal of heavy volumes of traffic from roads that are close to residential
The bypass will reduce traffic volumes in Stoke Gifford, whilst those additional properties in developments to the east of Stoke Gifford centre represent a smaller population group and will be
S Policy
TOKE GIFFORD BYPASS STUDY
Review and Scheme Appraisal
• ensure air quality in all other areas remains
better than national standards receptors could help to ensure that standards in non AQMAs will remain better than the national target limit. Score 3
close to free-flowing rather than stop-start traffic, so the net effect is likely to be a slight improvement in air quality. Score: 3
To improve accessibility: • improve accessibility for all residents to
educational services • improve accessibility for all residents to
health services • improve accessibility for all residents to
employment
The scheme does not have accessibility as an explicit objective. However the high peak hour traffic levels in the area is indicative of the demand for home to employment trips and therefore the scheme could well make a significant contribution to enhancing accessibility – albeit primarily by car. The removal of high volumes of traffic may also make access to local schools safer for children as long as there are cycling and walking facilities provided and that speeds on the traffic relieved roads are managed. Score 3
As detailed in earlier matrices, the scheme satisfies all of the objectives listed in this row. Score: 3
To improve the quality of life: • ensure quality of life is improved through the
other shared priority objectives, contributing towards the enhancement of public spaces and of community safety, neighbourhood renewal and regeneration, healthier communities, tackling noise and protecting landscape and biodiversity
• achieve balanced and sustainable communities
This is not an explicit objective of the scheme although there will be benefits related to noise reduction for some properties (perhaps counter balanced by an increase at others). If alternative modes are effectively encouraged then there will be health benefits associated with greater levels of walking and cycling. Score 2
Traffic conditions will be relieved in Stoke Gifford which will lead to a small environmental improvement within the village. However background traffic congestion across the wider network and the need for residents to travel between, say, Bradley Stoke, Filton and Horfield, does mean that there will remain a residual demand for travel through the village. Score: 2
Overall Assessment and Score The wide scope of the Provisional LTP objectives means that the scheme appears to fit less well with the relatively newer aspects of local transport planning such as accessibility and some aspects of the quality of life agenda. However the more traditional benefits of road schemes such as local congestion relief and safety improvements do tend to counter balance this. Score 3
The bypass scheme generally supports the JLTP objectives. It provides a local benefit to residents, pedestrians and cyclists in Stoke Gifford and complements the GBBN that proposes a showcase bus corridor through Stoke Gifford; the traffic relief suggested by the traffic model will contribute further to the aims and objectives of the GBBN, which is primarily to improve bus service reliability and to enhance the experience of bus passengers. Score: 3.
CONCLUSIONS 2.15 The policy review demonstrates that the Stoke Gifford bypass has a
reasonable degree of consistency with the various national, regional and local policy objectives. Table 2.7 summarises the summed average scores for the six policy documents that have been reviewed:
Table 2.7: Summary of Policy Scores
Policy Document Summed Average Score (out of 8)The Future of Transport: A Network for 2030 6 Regional Spatial Strategy 4 Regional Funding Allocations: Advice from the South West Region 4 Joint Replacement Structure Plan 7 Greater Bristol Strategic Transport Study 6 Greater Bristol Joint Local Transport Plan 6
2.16 In general terms, the scheme achieves higher scores against local objectives than regional objectives. This reflects the fact that it is essentially a local bypass scheme, albeit in the largest Strategic City and Town (SSCT) in the south west. There is also a good score against the Transport White Paper
2.17 The scoring in this policy review has also been relatively generous in that it assumes benefits to non car modes. Whilst it is certainly the case that the bypass can assist in delivering better bus services (through congestion relief) and multi-modal infrastructure improvements, it would be unwise to assume that such measures, on their own, will automatically deliver actual changes in travel behaviour away from the single occupancy private car.
2.18 In order to deliver against sustainable transport objectives the scheme needs to be set in its wider strategic context and it is particularly important to identify other capital funded schemes and revenue funded policy initiatives that will actively support travel by non car modes. Therefore the next Local Transport Plan and the longer term Greater Bristol Strategic Transport Study recommendations will be important for ensuring that the Stoke Gifford bypass proposals don’t simply encourage more traffic through the reduction of journey times for car drivers.
STOKE GIFFORD BYPASS STUDY Policy Review and Scheme Appraisal
3. Traffic Forecasting 3.1 The potential traffic impacts of the scheme in 2016 (assumed year of opening)
and 2031 (design year) have been forecast using the BATS2 transport model, which was developed for the Greater Bristol Bus Network Major Scheme Bid. This model and its validation against 2004 transport data are fully described in the “Model Development and Validation Report – 2004”, dated July 2005, which should be consulted for detailed technical information. The following paragraphs provide a brief overview of the model.
BATS2 MODEL 3.2 The BATS2 model was based on the original Bristol Area Transport Study
(BATS) model of the Bristol area which was developed for Bristol City Council (BCC) to appraise the proposed congestion charging scheme and associated improvements to the public transport network, including light rapid transit (LRT) options. As part of the updating process, the base year for the model was brought forward from 2001 to 2004, and the modelled highway network in the northern sector of Bristol was extended and refined using information drawn from SGC’s North Fringe traffic model.
3.3 The model is focussed on the Bristol urban area, bounded by the M5 to the west, the M4 to the north (with an extension along the A432 to Yate), the A4174 outer ring road to the east, and the Bristol City boundary to the south. Within this area, highway and public transport networks are defined in detail, road junctions are simulated for queues and delays, and a fine zoning system is employed to model patterns of trip movement. Outside this area, a coarser zoning system and network covers the rest of South Gloucestershire, North Somerset, and Bath and North-East Somerset.
3.4 It is clear from our assessment of potential scheme impacts that the BATS2 model covers a much wider area than that which would be affected by the Stoke Gifford bypass. Ideally therefore, the model should be cordoned to represent the area of influence of the scheme, and refined within this cordon to better represent local patterns of movement and travel choices. However, given the study time constraints, it was not possible to undertake this work, and the full model has been used for this preliminary assessment.
3.5 The BATS2 transport model is fully multi-modal, representing travel by all motorised modes. Logit functions calibrated from observed travel data or (where necessary) imported from other studies, are employed in a nested structure to forecast travel demand, including:
♦ levels of trip suppression resulting from increased traffic congestion, and induced traffic resulting from the provision of additional highway capacity;
♦ main mode choice between car, park and ride, and public transport;
♦ with congestion charging in place, the choice for car drivers between paying the charge, parking outside the charging zone and walking in, or retiming the journey to a lower tariff period;
♦ the choice for public transport users between bus, rail and LRT.
3.6 These choices are segmented by car availability and trip purpose, and are based on the generalised cost of travel by alternative modes, including travel time and monetary costs. For car users, these include vehicle operating
STOKE GIFFORD BYPASS STUDY Policy Review and Scheme Appraisal
costs (mainly fuel), parking charges, and time spent searching for a space and walking between car park and destination. For public transport users, the costs include wait time, walking time and fares.
3.7 The demand model is used to forecast trip movements by mode and purpose, based on input generalised costs. These matrices are combined to represent all-purpose movements, and assigned to the modelled highway and public transport networks, which are skimmed for travel costs. The resultant costs are then fed back to the demand model as part of an iterative procedure which seeks to balance travel demand and travel costs, and thus to reach a converged position.
3.8 Trip movements by road are converted from drivers and passengers to vehicles, based on average occupancy, and combined as follows:
♦ Light vehicles (cars and light goods vehicles);
♦ Heavy goods vehicles.
3.9 Two time periods are modelled, as follows:
♦ AM peak hour (0800-0900);
♦ Average inter-peak hour (1000-1600).
3.10 The BATS2 model does not have a PM peak hour component. Therefore, for the purposes of this appraisal, PM peak benefits have been ignored.
MODEL VALIDATION 3.11 Development and validation of the BATS2 model is fully documented in the
“Model Development and Validation Report – 2004”.
3.12 The BATS2 traffic model was calibrated using standard matrix estimation techniques, and validated against observed traffic flows and journey times, based on advice contained in the Design Manual for Roads and Bridges (DMRB).
Traffic Flow Comparisons 3.13 Traffic flow comparisons were based on three cordons (Inner Ring Road,
Outer Central, and Outer External), and five screenlines (Bristol North West Outer, River Avon, Bristol North West Inner, Bristol East, and Bristol South). For acceptability, DMRB requires that cordon and screenline totals should have a GEH value of less than 4, and that 85% of the individual links in each case should have a GEH of less than 5. However, given the scale and complexity of the BATS2 model, the consultants (Atkins) recommended that these individual link targets should be relaxed for the Outer External Cordon and all screenlines, and suggested that 85% of these links should have a GEH value of less than 7.
3.14 Information presented in the report for the AM peak hour showed that all cordons and screenlines achieved a GEH value of less than 4 based on total flows, indicating that modelled patterns of movement are broadly correct at strategic level. For individual links, all cordons and screenlines achieved GEH values of less than 7 in 85% of cases (save one at 83%), but the Inner Ring Road and Outer Central Cordons missed their targets of 85% with a GEH of less than 5. (They achieved 78% and 83% respectively). For the Bristol North West Outer and North West Inner screenlines, located in the vicinity of Stoke Gifford, about 80% of links have a GEH of less than 5. As a
STOKE GIFFORD BYPASS STUDY Policy Review and Scheme Appraisal
local model, this would not be adequate for DMRB approval, but is acceptable for a large urban area.
3.15 For the inter-peak model, all cordons and screenlines achieved a GEH value of less than 4 for total flows and in all cases 85% of links had a GEH value of less than 7. The Inner Ring Road cordon again missed the target of 85% of links with a GEH of less than 5 (it achieved 77%). However, most of the screenlines, including those for North West Bristol, had 85% of links with a GEH value of less than 5. On this basis, the inter-peak model is likely to be more reliable in the Stoke Gifford area than the AM peak model.
Journey Time Comparison 3.16 The DMRB recommends that modelled journey times should be within 15%
(or 1 minute) of the observed times on 85% of routes.
3.17 The “Model Development and Validation Report – 2004” compares modelled and observed journey times on nine routes surveyed in 2004. It shows that only 7 of 16 directional routes (44%) achieved the DMRB target in the AM peak hour, rising to 13 out of 17 (76%) in the average inter-peak hour. However, since most of the modelled journey times fall within the observed bounds, this was considered adequate for a large scale model of the city.
3.18 It should be noted that most of the nine observed routes are located well away from Stoke Gifford, except for the M32 route which validates well in both directions and both time periods. However, the general level of journey time validation achieved would not meet DMRB standards for a local model, and may not be sufficient to support an economic appraisal of the bypass scheme.
Validation Improvement 3.19 Given the time-scales for this study, it was not possible to develop a local
model of the Stoke Gifford area, or to undertake a significant revalidation of the BATS2 model. This was accepted by SGC officers and members at the meeting of 19 October 2005. However, we have attempted to improve the modelled highway network in the local area of the proposed scheme by refining saturation flows at a number of junctions and revising the allocation of centroid connectors.
3.20 Comparisons of modelled and observed flows at selected sites in the Stoke Gifford area (see Figure 3.1 for locations) are shown by direction for the AM and inter-peak hours in Tables 3.1 and 3.2. Table 3.2 shows that base year (2004) modelled flows in the inter-peak period meet the DMRB criteria based on the GEH statistic in 32 out of 35 cases (91%). However, Table 3.1 shows that the AM peak hour model meets these criteria in only 26 out of 37 cases (70%). On this basis, the peak hour model is probably not adequate at local level for scheme appraisal.
3.21 This is not a major concern given the preliminary nature of the appraisal at this stage. However, a further, more detailed appraisal in support of a major scheme bid would require significant improvements to the local model.
STOKE GIFFORD BYPASS STUDY Policy Review and Scheme Appraisal
FORECAST LAND-USE/NETWORK ASSUMPTIONS 3.22 The BATS2 model has been used to produce forecast AM peak hour and
average inter-peak hour trip matrices for 2016 (assumed year of opening of the Stoke Gifford bypass) and 2031 (the design year). In accordance with the SGC terms of reference, these forecasts have been based on Scenario F as recently defined by the JSTPU for the Greater Bristol Strategic Transport Study (GBSTS).
3.23 Key housing and employment allocations for this scenario are summarised in Table 3.3. It assumes that new dwellings would be built at a rate of 4625 per annum within the four Unitary Authorities, representing a 25% increase on the rate of development proposed in RPG10 and providing 138,750 additional homes between 2001 and 2031; and that employment opportunities would increase at a rate of 3166 jobs per annum, to provide an additional 95,000 jobs by 2031. Forecast trip-ends for Scenario F were provided by the GBSTS study team, and converted for input to the BATS2 model.
3.24 However, given the limited time-frame for the Stoke Gifford Bypass study and the uncertain status of the schemes proposed for the GBSTS Final Strategy, most of the GBSTS schemes have not been included in the BATS2 forecast networks. Instead, the forecasts have been based on the Do Something networks developed for the Greater Bristol Bus Network Major Scheme Business Case, assuming that the showcase bus corridors and associated infrastructure improvements (North Fringe Development Major Schemes) would go ahead and would be completed by 2016.
3.25 To some extent, this approach means that the forecast tests are based on an unsustainable scenario, in which accelerated development growth (Scenario F) is assumed to take place without associated improvements to the highway and public transport networks (GBSTS Final Strategy). This would tend to encourage greater car use, and may therefore overestimate the potential benefits of the Stoke Gifford bypass (by overestimating congestion in the Do Minimum case). However, it is considered unlikely to have a major affect on the operational and economic appraisals of the scheme at this stage, or on the overall findings of the study.
3.26 One scheme included in the GBSTS Final Strategy which may have a direct impact on the Stoke Gifford bypass is the proposed widening of the M4 between Junctions 19 (M32) and 20 (M5). Sensitivity tests have therefore been run to identify the diversionary affects of this scheme.
3.27 The BATS2 model has been run once for each forecast year and time period, based on Scenario F land-use assumptions and the Greater Bristol Bus networks, which include the proposed showcase bus corridors and associated infrastructure improvements but exclude the Stoke Gifford bypass. The matrices of highway-based trips resulting from this multi-modal forecasting procedure represent the reference case for the bypass study. These matrices have then been assigned to test networks excluding the bypass (Do Minimum case) and to a number of Do Something networks including alternative scheme alignments. This testing therefore assumes that the bypass would have no impact on mode choice.
STOKE GIFFORD BYPASS STUDY Policy Review and Scheme Appraisal
Table 3.3 – Summary of Scenario F Housing and Employment Forecasts Scenario F increases in housing and employment between 2001 and 2031:
SCHEME ALTERNATIVES FOR TESTING 3.28 Alternative bypass schemes tested in the model are shown in Figure 3.2.
These were identified by SGC, based on a desktop analysis of engineering opportunities and constraints. Scheme costs were also provided by SGC.
3.29 All four alternative schemes would provide a new dual-carriageway link from the roundabout at the southern end of Great Stoke Way to a signalised junction with the A4174 Avon Ring Road to the east of Coldharbour Lane. All would cross the railway line at a single bridged location. Other key features of the schemes are as follows:
♦ The Purple Route would take the more easterly of the two alignments to the south of the railway line. It would have an at-grade crossing of Hambrook Lane, which is assumed to be a roundabout allowing all turning movements. Further south, it would have a roundabout junction with the access road to the Harry Stoke development, and would link to the more easterly of the two ARR junction locations;
♦ The Pink Route would take the more westerly of the two alignments, requiring an additional roundabout junction at the north end of the scheme, and would link to the more westerly of the two ARR junction locations. It would have a roundabout connection to Harry Stoke, but no connection with Hambrook Lane;
♦ The Turquoise Route would be similar to the Pink Route but would link to the more easterly ARR junction;
♦ The Blue Route would be similar to the Purple Route, but would have a signalised junction with Hambrook Lane, allowing straight-ahead movements only (i.e. no movements between the bypass and Hambrook Lane), and would link to the more westerly ARR junction.
3.30 The four alternative schemes were coded into the test networks in detail, so that the model could simulate traffic movements through junctions and thus forecast their impacts on queues and delays. Roundabouts were assumed to be similar in dimension and capacity to those already in place on Great Stoke Way. The layout and signal timings for the proposed ARR junction were based on those already tested for the Greater Bristol Bus Network Major Scheme Bid (which included the junction to provide access for the Harry Stoke development).
3.31 The eventual route choice for the bypass will be influenced by a number of external developments, including:
• Proposals for a special school, currently being investigated by SGC Children & Young People which may be located in Stoke Gifford adjacent to existing development which would not allow for the alignment of Purple and Blue routes; the school is located at the northern end of these routes, immediately to the south of the roundabout junction with Great Stoke Way;
• Development proposals for Harry Stoke;
• North Fringe major schemes;
• Greater Bristol Bus Network; and
• Future RSS housing allocations for Harry Stoke.
STOKE GIFFORD BYPASS STUDY Policy Review and Scheme Appraisal
Figure 3.2 – Alternative Options for Stoke Gifford Bypass
4.1 The BATS2 model has been used to forecast the traffic impacts of the proposed Stoke Gifford bypass during the AM peak and average inter-peak hours in future years 2016 and 2031. Forecast land-use assumptions for both future years are based on Scenario F, which was developed by the JSPTU for the Greater Bristol Strategic Transport Study, assuming that the rate of housing and employment growth would be accelerated above RPG10 levels.
4.2 However, given study time constraints and the uncertain status of transport improvements proposed as part of the GBSTS Final Strategy, most of the GBSTS schemes have not been included in the forecast test networks. Instead, the tests have been based on future year Do Something networks developed for the Greater Bristol Bus Network Major Scheme Business Case.
4.3 Four alternative scheme alignments, defined by SGC and shown in Figure 3.2, have been tested in the model, along with a Do Minimum case which excludes a bypass. The BATS2 multi-modal model was run for each year and time period to forecast the level of traffic demand in the Do Minimum network, allowing that increased traffic congestion would cause some drivers to switch modes or suppress trips. Scheme tests were then run using the same (fixed) demand matrix for each time period, assuming that the bypass would not induce any additional trips, and that the potential impacts would therefore be limited to re-routing effects.
TRAFFIC GROWTH 4.4 Forecast trip totals for 2004, 2016 and 2031 are presented in Tables 4.1-4.4.
These show that light vehicle traffic demand in the Bristol area, after allowing for modal transfer and trip suppression, would increase by 16%-18% from 2004 to 2016, and by 29%-31% from 2004 to 2031. Heavy vehicles would grow at a higher rate, but form a relatively small proportion of the overall vehicle flow.
FORECAST NETWORK PERFORMANCE 4.5 Traffic growth would have a significant impact on levels of congestion in the
Do Minimum network, as shown by the increase in over-capacity queued time. Average speeds in the AM peak hour, based on the full Bristol network, would drop from 42.1 kph in 2004 to 28.6 kph in 2016, and to 19.6 kph in 2031. Average speeds in the inter-peak period would similarly drop from 50.6 kph in 2004 to 44.6 kph in 2016, and to 34.1 kph in 2031.
4.6 Within the local area network (north-west Bristol, including Stoke Gifford, Bradley Stoke, Patchway, Aztec West, Cribbs Causeway and Filton), average speeds are currently higher (by 6-9 kph) than those for the whole of Bristol. However, this difference is likely to become less significant with time, and would be largely eroded by 2031. In fact, the 2031 forecasts suggest that average inter-peak speeds in this area may then be lower than the Bristol average because of increased congestion at Cribbs Causeway.
4.7 Table 4.1 shows that the Stoke Gifford bypass would have a beneficial impact on peak hour congestion in 2016, reducing total travel times within the local area network by 300-500 pcu-hours. However, forecast travel distance would
STOKE GIFFORD BYPASS STUDY Policy Review and Scheme Appraisal
increase as a result of drivers taking longer routes in order to gain access to the bypass. The net result is that average speeds in the local area would increase by about 1 kph, from about 33 kph to about 34 kph. Overall average speeds in Bristol would increase by 0.3 kph.
4.8 In 2031, the scheme would reduce total AM peak hour travel times in the local area network by 600-1000 pcu-hours, and increase average speeds by about 1 kph, from 21 kph to 22 kph (see Table 4.3). Average speeds in Bristol as a whole would increase by 0.4-0.5 kph.
4.9 From Tables 4.2 and 4.4, it is clear that the Stoke Gifford bypass would have a more marginal impact on travel times, distances, and average speeds in the inter-peak period, either in 2016 or 2031. This is because traffic flows in the inter-peak period are only about 70% of those in the peak hour, and would not even by 2031 have grown to current peak hour levels. Therefore, the scheme would offer less congestion relief outside the peak hours.
4.10 All of the bypass options demonstrate broadly similar effects, and there is little to choose between them in terms of network performance, based on either the local area network or Bristol as a whole.
FORECAST TRAFFIC FLOWS 4.11 Forecast AM peak and inter-peak traffic flows on selected links are presented
for 2016 and 2031 in Tables 4.5-4.8. Figure 4.1 shows the locations of these sites, as well as a number of others which were identified following a meeting with members on 21 March 2006. Forecast flows for all of these sites in the 2016 AM peak and inter-peak hours are presented in Appendix A and summarised in paragraphs 4.28-4.33.
4.12 Tables 4.5-4.8 show forecast traffic flows, in vehicles per hour summed over two directions, for the Do Minimum scenario and Do Something scheme options, so that the impacts of the bypass can be determined. The results of sensitivity tests, which assume that the M4 would be widened between Junctions 19 (M32) and 20 (M5), as recommended in the GBSTS Final Strategy, are also included in the tables.
4.13 Based on the traffic forecasts shown in Table 4.5, the Stoke Gifford bypass would attract 2-way flows of between 1610 and 1970 vehicles per hour (vph) in the 2016 peak hour. Flows would be at the lower end of this range if no junction was provided at Hambrook Lane (as for the Pink and Turquoise options); and at the higher end of the range if a full roundabout junction was provided (as for the Purple option). By 2031, traffic growth would have increased these peak hour flows to between 1750 vph and 2150 vph (see Table 4.7).
4.14 Tables 4.6 and 4.8 show that forecast traffic flows on the bypass during the inter-peak period would be significantly lower than in the peak hour, with a maximum flow of about 660 vph in 2016 and 920 vph in 2031.
4.15 On this basis, a single carriageway road of 10 metre width would be more than adequate to accommodate forecast traffic demand to 2031. This would significantly reduce the cost of the scheme, assuming that SGC would not want to make provision for later construction of a Winterbourne bypass.
4.16 Traffic attracted to the scheme would increase peak hour flows on southern sections of Bradley Stoke Way by 250 - 450 vph in 2016, rising to 550 – 650 vph in 2031. Two way flows would then be almost 2000 vph, representing a 65%-75% increase on current levels. However, these impacts are localised
STOKE GIFFORD BYPASS STUDY Policy Review and Scheme Appraisal
and quickly dissipate with distance from the scheme. As a result, peak hour flows on northern sections of Bradley Stoke Way (i.e. already congested in 2006) would be increased by less than 250 vph in both 2016 and 2031.
4.17 Traffic flows on Winterbourne Road (to the west of Bradley Stoke Way) would also increase by up to 500 vph in the 2016 AM peak hour. However, the increase in 2031 would be less than 300 vph, suggesting that increased congestion in the local area would discourage access to the scheme via this route, and encourage greater use of Bradley Stoke Way (noted above).
4.18 Peak hour traffic flows on Old Gloucester Road to the north of Winterbourne Road would be reduced by up to 170 vph in 2016 and up to 310 vph in 2031. In both cases, the Purple Route would offer the greatest relief. Old Gloucester Road to the south of Winterbourne Road would also benefit from reduced flows in 2016.
4.19 Most of the bypass options would reduce peak hour traffic on Hambrook Lane to the east of the scheme by about 100 vph in both 2016 and 2031. This is evident even for the Purple Route which provides an all-movement junction with Hambrook Lane. As a roundabout, this junction would give priority to traffic on the bypass and cause delay for vehicles on the minor approaches, sufficient to discourage some rat-running traffic from using the lane. Signalisation of this junction in the Blue Route option would potentially cause greater delay to traffic on Hambrook Lane, encouraging significant diversion away from this route. The model forecasts suggest that some of this traffic would divert to Beacon Lane and Winterbourne Road. Forecast traffic flows on Hambrook Lane to the west of the bypass would similarly be reduced if a junction were provided.
4.20 On the basis of these varying traffic model results, it will be necessary to investigate the form of any potential junction with Hambrook Lane.
4.21 At the southern end of the bypass, traffic attracted to the scheme would increase peak hour flows through the Harry Stoke development on its access road by 450 – 550 vph in 2016, and by 600 – 700 vph in 2031, despite traffic calming on this road which would reduce speeds below 30 mph.
4.22 Peak hour flows on the A4174 ARR to the east of the bypass would also increase significantly by 600 – 700 vph in 2016, and 750 – 850 vph in 2031. However, the model shows that this additional traffic could be accommodated at the signalised ARR junction without imposing delays of more than 1 minute on any movement; minimal peak hour queues would therefore occur at this location in both 2016 and 2031.
4.23 The bypass would have little impact on M32 Junction 1 in the 2016 AM peak, adding a few seconds only to vehicles on the eastbound entry. Traffic growth to 2031 would be more difficult to accommodate, and the increased flow on the A4174 ARR would lengthen peak hour queues and add up to 2 minutes of additional delay to vehicles on the eastbound approach to M32 Junction 1, compared with the Do Minimum case. However, these queues would not stretch back to the junction with the bypass, and the ARR itself would have sufficient link capacity to accommodate the forecast flows. Also, it may be possible to reduce queuing on the approach by adjusting the signal timings at the motorway junction (not tested in the model).
4.24 To the west of the bypass, forecast flows on the A4174 ARR would decrease as a result of the scheme. Nevertheless, westbound flows with the scheme in place would exceed the available capacity at the Coldharbour Lane junction.
STOKE GIFFORD BYPASS STUDY Policy Review and Scheme Appraisal
Long queues would form on the approach, although these would not extend back to the bypass junction even by 2031; and delays of about 2 minutes per vehicle would occur in 2016, increasing to almost 5 minutes by 2031.
4.25 Within Stoke Gifford itself, Brierly Furlong would get some limited relief from the scheme, while peak hour flows on Westfield Lane would generally be reduced by about 100 vph in 2016, and 200 – 300 vph in 2031 (given some diversion back to Brierly Furlong). Peak hour traffic on Hatchet Road would also be reduced by 150 – 300 vph in both 2016 and 2031. Congestion within the village centre would therefore be reduced accordingly. For the Blue Route option, these impacts would be even greater because more traffic would divert away from Hambrook Lane (as noted above).
4.26 The model forecasts suggest that all four route options would have broadly similar impacts on traffic routing, and would help to relieve the centre of Stoke Gifford. There is little to choose between them in this respect. The forecasts also suggest that a junction with Hambrook Lane is unlikely to cause a major increase in rat-running.
4.27 Tables 4.5-4.8 also include forecast flows assuming that the M4 would be widened between Junctions 19 and 20. These show that the proposed widening would have little impact on traffic using the bypass, or on other roads in the Stoke Gifford local area.
4.28 Figure 4.2 shows the forecast effects of the Purple Route option on 2016 AM peak hour traffic flows. It confirms that the scheme would increase traffic flows on Bradley Stoke Way, the Harry Stoke development access road, and the Avon Ring Road between the bypass and M32 Junction 1. Some of this traffic would be attracted from the M5/M4/M32 route between M5 Junction 16 and M32 Junction 1. Other roads relieved of traffic would include Hatchet Road, Brook Way, Brierley Furlong, Westfield Lane and Hambrook Lane. The scheme would also cause traffic to divert from Old Gloucester Road to B4058 Winterbourne Hill.
4.29 Forecast traffic using the Purple Route option is identified in Figure 4.3 for the 2016 AM peak hour. This shows that the bypass would be most attractive for traffic between the Bradley Stoke area and central Bristol, which would route via the scheme, the ARR, and M32.
FORECAST TRAFFIC EFFECTS BY AREA 4.30 Forecast 2016 traffic flows (peak and inter-peak) are shown for all links
(identified in Figure 4.1) in Appendix A. These have been grouped into a number of broad sectors, which are discussed below.
4.31 Routes which run broadly parallel to the Stoke Gifford bypass, like Hatchett Road, Hambrook Lane, Westfield Lane, Brierly Furlong and Old Gloucester Road would generally be relieved by the scheme, as noted above. This will provide an environmental improvement for residents, pedestrians and cyclists on these routes.
4.32 To the north and west, the bypass would attract additional traffic to routes like Bradley Stoke Way and Winterbourne Road. However, this would relieve other roads in the local area, notably Baileys Court Road, Orpheus Avenue and Braydon Avenue, i.e. through traffic is diverted to more appropriate routes. Some traffic would also be attracted from the A38.
4.33 Immediately to the west of the bypass, traffic flows on the A4174 Avon Ring Road would be reduced by up to 250 vph, some of which would transfer to
STOKE GIFFORD BYPASS STUDY Policy Review and Scheme Appraisal
Great Stoke Way and the Harry Stoke Link Road. Flows on the A38 to the north and south of the ARR would also be reduced.
4.34 To the south, the bypass would increase peak hour traffic flows on the A4174 ARR west of the M32 by up to 700 vph, as noted above. This would have limited impact in 2016 (as discussed in paragraph 4.23), and would in part be compensated by a reduction of 300 – 400 vph on the ARR to the east of the M32, which reflects a shift of traffic from the B4058 (Bristol Road and Winterbourne Hill) to the bypass. The M32 itself would be little affected by the scheme, since forecast traffic flows would be constrained by the available capacity whether or not the bypass scheme is implemented.
4.35 To the north and east of the bypass, High Street, Dragon Road and Down Road in Winterbourne would attract slightly higher traffic flows. However, this would be compensated by significant reductions in Hambrook Lane, Hicks Common Road, Winterbourne Hill and the B4058 Bristol Road. Flows on Beacon Lane would increase by over 100 vph. With the bypass in place, this route would carry more traffic to and from the north via High Street and less traffic to and from the south via Winterbourne Hill. The effects of this change can also be seen in Figure 4.2. This may place more stress on the Beacon Lane/High Street junction, but the reduction in through traffic, especially northbound on Winterbourne Hill may result in little net change in queue and delay at the junction. The A432 Badminton Road would be little affected by the scheme.
CHANGES IN BUS JOURNEY TIMES 4.36 Appendix B presents a summary of the net changes in overall journey time for
buses generally passing through the Stoke Gifford and Abbey Wood areas. The bus routes, route number and frequencies are those assumed for Corridor 4 of the Greater Bristol Bus Network (which follows bus route 73 between Gloucester Road (at Filton Avenue), Bradley Stoke and Cribbs Causeway (The Mall)) in the forecast year 2010. These routes are shown schematically in Figure 4.4. It should be noted that some bus routes have already changed since the GBBN report was published in June 2005.
4.37 No bus routes are proposed to use the bypass. This is because to do so would mean services between Bradley Stoke, Stoke Gifford and Bristol could not reasonably serve UWE and the Abbey Wood area which would need to be served during the inter peak periods in particular when passenger flows are lower. This does not mean that peak hour only services could not be introduced to use the bypass if adequate demand between Bradley Stoke and Bristol could be realised (for example, diversion of Route X73 could be considered).
4.38 Appendix B shows that the reduction in traffic flows and congestion on Hatchet Road and Brierly Furlong through Stoke Gifford gained by the bypass generally reduces southbound bus journey times using these sections in the AM peak by between one and three minutes (varying by bypass alignment option). Northbound bus journey time reductions are about one minute in this time period. Inter peak journey times are not affected as traffic flows are lower across the whole area. Similar reductions in journey times could be expected in the PM peak period, although this has not been modelled.
4.39 Changes in journey time for all other routes shown in Figure 4.4 are marginal and are not affected by the bypass.
STOKE GIFFORD BYPASS STUDY Policy Review and Scheme Appraisal
FULL NETWORK Forecast Matrices (vehs) Light vehicles 138,259 163,287 163,287 163,287 163,287 163,287Heavy vehicles 6,327 7,620 7,620 7,620 7,620 7,620Total 144,586 170,907 170,907 170,907 170,907 170,907 Simulation Network Running time (pcu-hrs) 20,001 25,393 25,419 25,423 25,392 25,319Transient queued time 4,822 6,730 6,744 6,774 6,749 6,754Over-capacity queued time 2,606 15,072 14,719 14,611 14,881 14,814Total Travel Time (pcu-hrs) 27,430 47,195 46,882 46,807 47,022 46,887Total Travel Distance (pcu-kms) 1,155,500 1,351,019 1,353,921 1,353,740 1,352,940 1,350,245Average Speed (kph) 42.1 28.6 28.9 28.9 28.8 28.8 Convergence after iteration 9 17 16 17 14 13Delta function (%) 0.178 0.324 0.361 0.366 0.333 0.351% links changing by <5% 99.5 95.1 94.7 94.7 94.7 94.6 LOCAL AREA NETWORK Simulation Network Running time 4,954 6,521 6,531 6,523 6525 6,476Transient queued time 914 1,369 1,385 1,388 1,387 1,374Over-capacity queued time 562 3,767 3,218 3,281 3,297 3,496Total Travel Time 6,430 11,658 11,135 11,192 11,209 11,347Total Travel Distance 328,547 383,341 385,825 385,517 385,419 383,914Average Speed (kph) 51.1 32.9 34.6 34.4 34.4 33.8 Notes: 1. pcu = passenger car unit (average pcu value of heavy goods vehicles = 2.4)
2. Travel times are in pcu-hours, distances in pcu-kms 3. Average speed = Total Travel Distance / Total Travel Time 4. The level of convergence of each assignment is defined by the delta function (which measures the %
difference between assigned costs and minimum costs), and the % of links with a flow difference of <2% between successive assignment-simulation loops
STOKE GIFFORD BYPASS STUDY Policy Review and Scheme Appraisal
FULL NETWORK Forecast Matrices (vehs) Light vehicles 100,318 116.381 116.381 116.381 116.381 116.381Heavy vehicles 6,903 8.313 8.313 8.313 8.313 8.313Total 107,221 124,694 124,694 124,694 124,694 124,694 Simulation Network Running time (pcu-hrs) 14,620 17,665 17,635 17,646 17,630 17,662Transient queued time 3,382 4,533 4,514 4,529 4,519 4,544Over-capacity queued time 462 1,879 1,901 1,927 2,009 1,825Total Travel Time (pcu-hrs) 18,464 24,077 24,050 24,102 24,157 24,032Total Travel Distance (pcu-kms) 934,012 1,075,024 1,074,853 1,074,645 1,074,185 1,075,594Average Speed (kph) 50.6 44.6 44.7 44.6 44.5 44.8 Convergence after iteration 9 7 6 7 6 7Delta function (%) 0.146 0.154 0.172 0.186 0.180 0.164% links changing by <5% 99.8 97.9 94.8 97.9 94.7 97.1 LOCAL AREA NETWORK Simulation Network Running time 2,894 4,695 4,689 4,684 4,683 4,690Transient queued time 543 945 938 938 937 946Over-capacity queued time 96 691 639 700 721 686Total Travel Time 3,532 6331 6267 6,323 6,342 6,323Total Travel Distance 201,360 316,012 316,397 315,976 316,086 316,312Average Speed (kph) 57.0 49.9 50.5 50.0 49.8 50.0 Notes: 1. pcu = passenger car unit (average pcu value of heavy goods vehicles = 2.4)
2. Travel times are in pcu-hours, distances in pcu-kms 3. Average speed = Total Travel Distance / Total Travel Time 4. The level of convergence of each assignment is defined by the delta function (which measures the %
difference between assigned costs and minimum costs), and the % of links with a flow difference of <2% between successive assignment-simulation loops
STOKE GIFFORD BYPASS STUDY Policy Review and Scheme Appraisal
FULL NETWORK Forecast Matrices (vehs) Light vehicles 138,259 180,478 180,478 180,478 180,478 180,478Heavy vehicles 6,327 9,438 9,438 9,438 9,438 9,438Total 144,586 189,916 189,916 189,916 189,916 189,916 Simulation Network Running time (pcu-hrs) 20,001 27,157 27,288 27,208 27,306 27,210Transient queued time 4,822 7,130 7,219 7,151 7,213 7,175Over-capacity queued time 2,606 36,767 35,211 35,537 35,671 35,697Total Travel Time (pcu-hrs) 27,430 71,054 69,718 69,896 70,190 70,082Total Travel Distance (pcu-kms) 1,155,500 1,394,205 1,401,809 1,398,689 1,402,419 1,400,586Average Speed (kph) 42.1 19.6 20.1 20.0 20.0 20.0 Convergence after iteration 9 20 20 17 18 22Delta function (%) 0.178 0.620 0.357 0.557 0.450 0.420% links changing by <5% 99.5 94.5 94.9 94.7 94.6 94.6 LOCAL AREA NETWORK Simulation Network Running time 4,954 6,629 6,675 6,675 6,681 6,631Transient queued time 914 1,452 1,507 1,485 1,503 1,488Over-capacity queued time 562 9,972 9,002 9,035 9,212 9,352Total Travel Time 6,430 18,053 17,187 17,197 17,398 17,472Total Travel Distance 328,547 378,833 383,622 382,971 383,538 382,435Average Speed (kph) 51.1 21.0 22.3 22.3 22.0 21.9 Notes: 1. pcu = passenger car unit (average pcu value of heavy goods vehicles = 2.4)
2. Travel times are in pcu-hours, distances in pcu-kms 3. Average speed = Total Travel Distance / Total Travel Time 4. The level of convergence of each assignment is defined by the delta function (which measures the %
difference between assigned costs and minimum costs), and the % of links with a flow difference of <2% between successive assignment-simulation loops
STOKE GIFFORD BYPASS STUDY Policy Review and Scheme Appraisal
FULL NETWORK Forecast Matrices (vehs) Light vehicles 100,318 129,519 129,519 129,519 129,519 129,519Heavy vehicles 6,903 10,297 10,297 10,297 10,297 10,297Total 107,221 139,816 139,816 139,816 139,816 139,816 Simulation Network Running time (pcu-hrs) 14,620 19,230 19,210 19,225 19,169 19,209Transient queued time 3,382 5,166 5,160 5,175 5,156 5,186Over-capacity queued time 462 8,796 8,639 8,694 8,883 8,711Total Travel Time (pcu-hrs) 18,464 33,191 33,009 33,095 33,208 33,106Total Travel Distance (pcu-kms) 934,012 1,131,031 1,130,924 1,131,906 1,129,696 1,131,204Average Speed (kph) 50.6 34.1 34.3 34.2 34.0 34.2 Convergence after iteration 9 9 8 8 8 8Delta function (%) 0.146 0.294 0.209 0.232 0.280 0.411% links changing by <5% 99.8 95.4 95.9 94.5 94.9 94.6 LOCAL AREA NETWORK Simulation Network Running time 2,894 5,125 5,131 5,130 5,106 5,127Transient queued time 543 1,145 1,138 1,155 1,142 1,157Over-capacity queued time 96 6,378 6,290 6,225 6,246 6,273Total Travel Time 3,532 12,649 12,560 12,512 12,496 12,557Total Travel Distance 201,360 326,114 327,609 327,328 327,225 327,263Average Speed (kph) 57.0 25.8 26.1 26.2 26.2 26.1 Notes: 1. pcu = passenger car unit (average pcu value of heavy goods vehicles = 2.4)
2. Travel times are in pcu-hours, distances in pcu-kms 3. Average speed = Total Travel Distance / Total Travel Time 4. The level of convergence of each assignment is defined by the delta function (which measures the %
difference between assigned costs and minimum costs), and the % of links with a flow difference of <2% between successive assignment-simulation loops
STOKE GIFFORD BYPASS STUDY Policy Review and Scheme Appraisal
5. Economic Appraisal 5.1 A preliminary economic appraisal of the proposed Stoke Gifford bypass
scheme has been undertaken for all four of the alternative alignments outlined in Chapter 3.
5.2 Traffic forecasts for 2016 (assumed opening year of the scheme) and 2031 (design year), representing the AM peak and average inter-peak hours, have been input to the DfT’s TUBA and COBA programs to assess the transport efficiency and accident benefits of the scheme. These benefits have then been compared against the costs of construction to determine its net present value (NPV) and the benefit/cost ratio (BCR).
CONSTRUCTION COSTS 5.3 The TUBA program has been used to compare the user benefits of the Stoke
Gifford bypass scheme with its costs, including:
♦ ♦ ♦ ♦
the costs of construction; land and property costs; preparation and supervision costs; allowances for risk and optimism bias.
5.4 Delay costs during construction are likely to be small, given that most of the scheme would be constructed off line, and have therefore been ignored. Maintenance costs have also been ignored at this stage of the appraisal process.
5.5 The costs of construction, based on current (2006) prices, are itemised in Table 5.1. These were provided by SGC.
Main Works Costs 5.6 The main works cost is estimated to be between £5.72m and £8.83m,
depending on the alignment. This covers all earthworks, road and footpath construction, drainage, structures (including the bridge over the railway line), signing, lighting, landscaping, and environmental mitigation. Ancillary and other works would increase the total construction cost to between £6.45m and £9.28m.
5.7 It is assumed that the developer of the proposed Harry Stoke development would provide for the construction of a suitable single carriageway access road into the site from a signalised junction with the A4174 ARR. On this basis, the construction costs for the bypass at its southern end include only for an additional single carriageway (for conversion to dual standard), and a roundabout at the junction with the access road immediately to the east of the Harry Stoke site.
Land and Property Costs 5.8 Land and property costs are estimated to be between £7.43m and £8.72m,
based on current (2006) prices. This includes costs for re-housing, and compensation for mineral and other rights.
STOKE GIFFORD BYPASS STUDY Policy Review and Scheme Appraisal
Preparation and Supervision Costs 5.9 Preparation costs are estimated by SGC to be between £0.39m and £0.59m
(at 2006 prices), which represents 2.6% - 3.5% of the construction and land costs.
5.10 Supervision costs are estimated to be between £0.26m and £0.40m (at 2006 prices), representing 1.7% - 2.4% of construction and land costs. This is also significantly less than the HA default of 5%. Allowance for Risk and Optimism Bias
5.11 SGC have included a 10% contingency in the total works cost to allow for uncertainty. An allowance for optimism bias has also been included, based on DfT advice. This represents 25% of total works, supervision, and preparation costs.
Table 5.1 – Scheme Costs
Cost Category Cost (£000’s)
Purple/Blue Pink/Turquoise
A Main Works Contract 5,715 8,828
B Survey & Ancillary Works 407 352
C Work by Other Authorities 330 99
Total Works Cost 6,452 9,279
D Supervision Costs 260 401
E Preparation Costs 394 592
F Land (cost estimate includes mineral and other compensation) 8,721 7,427
G Allowance for Optimism Bias 1,776 2,568
Total 17,602 20,267 Notes: 1. All costs in £000s, based on current (2006) prices.
2. Costs for Main Works, Survey & Ancillary Works, and Work by Other Authorities include a 10% contingency.
3. Optimism Bias assumed to be 25% of total works, supervision and preparation costs.
PRESENT VALUE COSTS 5.12 TUBA requires that all costs (and benefits) are measured at constant 2002
prices. The costs shown in Table 2.1 have therefore been adjusted by TUBA, to remove the effects of inflation, as indicated by the relative change in the retail price index (RPI). Construction costs have also been adjusted by the relative price factor (RPF) which takes account of the change in the cost of road construction relative to the general price level.
5.13 Scheme costs have been allocated to future years, assuming that construction would start in 2014 and that the scheme would open in 2016. Construction costs have been distributed through the construction period as follows, based on DMRB advice:
STOKE GIFFORD BYPASS STUDY Policy Review and Scheme Appraisal
5.14 Land and property costs would be incurred largely at the start of construction, in 2014. Preparation costs would be spread through the years up to 2014; supervision costs would be spread through the construction period from 2014 to the 2016 opening year.
5.15 These costs (and benefits) have then been converted by TUBA to ‘present values’, based on the principle that, generally, society prefers to receive goods and services now, rather than later, and to defer costs to future generations. A discount rate of 3.5% per annum is used for the first 30 years of the appraisal (3.0% thereafter), based on the advice of the Treasury’s Green Book.
TRANSPORT ECONOMIC EFFICIENCY BENEFITS 5.16 The economic benefits of the scheme have also been calculated by TUBA,
based on input data extracted from the forecast traffic assignments for 2016 (opening year) and 2031 (design year).
5.17 The TUBA program uses input trip matrices, together with associated time and distance skims of the modelled network to calculate the travel time costs and operating costs of all vehicles in the Do Minimum and Do Something scenarios, for each of the modelled time periods. These hourly costs are expanded, based on input annualisation factors, and combined to estimate annual costs for 2016 and 2031. Annual costs for other years are interpolated, and summed over the 60 year assumed life of the scheme, in accordance with DfT advice. The program then compares these Do Minimum and Do Something travel costs to determine the user benefits for consumers (non-work trips) and business users (work trips, including HGVs).
TUBA INPUTS 5.18 The traffic forecasts were interrogated to provide matrices of trips, journey
times and journey distances for each:
modelled year (2016 opening year and 2031 design year); time period (AM peak hour and average inter-peak hour); scenario (Do Minimum and Do Something); and vehicle type (light and heavy vehicles).
5.19 Matrices of journey times and distances were extracted from the models based on the combined routes saved during the assignments, and therefore represent the average travel times and distances for all trips through the network. (They were not based on single least cost trees). These matrices have been input to TUBA for each of the modelled time periods.
5.20 Annualisation factors represent the number of hours in the year that would be similar in traffic terms to each of the hours modelled. For this appraisal, they have been drawn from the TUBA files set up for the appraisal of the Greater Bristol Bus Network, as follows:
AM peak hour factor – 759, assuming that conditions represented by the AM peak hour model would extend over a 3 hour morning peak period, for all 253 working days of the year;
STOKE GIFFORD BYPASS STUDY Policy Review and Scheme Appraisal
♦ Inter-peak hour factor – 1518, assuming that the inter-peak model represents the 6 hour inter-peak period (10:00-16:00) for all 253 working days.
5.21 Benefits which would accrue during the PM peak period, during night-times and at weekends have been ignored.
5.22 Other inputs to the TUBA program are drawn from the DfT’s Transport Economics Note (TEN), and are provided as default values by the TUBA program.
5.23 Based on these input parameters and the forecast traffic data extracted from the model assignments, TUBA calculates the annual time and vehicle operating cost benefits of the scheme for the 2016 opening year and 2031 design year. Benefits for the intervening years are interpolated from the modelled years. Those for the years 2031-2075 are calculated assuming that there would be no traffic growth beyond 2031. Annual benefits for each year in the appraisal period are then discounted to present year (2002) values, and combined.
ECONOMIC BENEFITS OF THE SCHEME 5.24 The economic benefits of the scheme, as calculated by TUBA, are
summarised in Table 5.2. This shows that the total discounted present value of the benefits (PVB) would be between £461 and £663 million at 2002 prices, over the 60 year appraisal period. This range is greater than anticipated, given the relatively small differences between the scheme options, and will to some extent reflect high levels of congestion and routing instability in the future year assignments. Sector analysis has shown that only 60% of these benefits would accrue to road users passing through or operating within the local area, with 40% going to other road users outside this area. However, in all cases, the scheme would still generate very significant benefits for users.
Table 5.2 – Economic Efficiency Benefits of the Stoke Gifford Bypass
Benefits (£000s) TRANSPORT ECONOMIC EFFICIENCY BENEFITS (TEE) Purple Pink Turquoise Blue
Consumers User Benefits
- Travel Time 246,938 230,317 172,270 172,899 - Vehicle Operating Costs 7,964 9,641 7,112 6,620 - User Charges - During Maintenance
Net Consumer Benefits 254,902 239,958 179,382 179,519 Business User Benefits
- Travel Time 400,176 369,776 277,960 281,344 - Vehicle Operating Costs 15,886 17,093 10,268 10,100 - User Charges - During Maintenance
Net Business Benefits 416,065 386,869 288,228 291,444 Total Present Value of Benefits (PVB) 662,818 618,951 461,742 462,121
STOKE GIFFORD BYPASS STUDY Policy Review and Scheme Appraisal
3. Based on a 60 year appraisal period (2016–2075)
5.25 Business benefits would contribute about 60% of the total PVB; consumer (non-work) benefits would contribute about 40%. Table 5.2 shows that time savings make up the majority of these user benefits, reflecting the significant level of congestion relief that the scheme would provide.
5.26 The TUBA program compares the discounted travel time and vehicle operating cost benefits of the Stoke Gifford bypass against the discounted costs of constructing the scheme, in order to determine its net present value (NPV) and Benefit/Cost Ratio (BCR).
ACCIDENT BENEFITS 5.27 Forecast traffic flows for 2016 (opening year) and 2031 (design year) have
been input to the DfT’s COBA program to estimate the number of accidents and casualties by severity that would be saved by the scheme over the 60 year appraisal period, 2016-2075. These savings have then been converted (by the program) to 2002 monetary values, and discounted to 2002 based on the recommended annual discount rates of 3.5% (for the first 30 years) and 3.0% (thereafter).
5.28 Forecast Do Minimum and Do Something traffic flows for 2016 and 2031 were extracted from the traffic model assignments for each time period. These were combined to estimate AADT flows for input to COBA. Traffic flows for other years in the 60 year appraisal period have been interpolated by the program, which projects backwards and forwards from the modelled years based on the National Road Traffic Forecasts (NRTF). No growth was assumed beyond 2031.
5.29 The DMRB recommends that observed accident data covering a 5 year period should be used to determine existing accident rates for appraisal purposes. However, this information generally takes some time to obtain from the relevant authorities, organise for the study area, and analyse for input to COBA. Given the short time-frame for the study, this appraisal has therefore been based on default accident rates supplied by the program.
5.30 Although the BATS2 model covers the whole of Bristol, a localised COBA network has been developed to include only that part of the road network which would be directly affected by the proposed Stoke Gifford bypass. This area, defined by comparing the SATURN model assignments for the Do Something and Do Minimum scenarios, is shown in Figure 5.1
5.31 The COBA program has used the default accident rates and forecast traffic flows to calculate the number of accidents and casualties for the Do Minimum and Do Something scenarios, for each year of the appraisal period. Accident savings have then been determined by comparing the number of forecast accidents in each year, and summing over all years. These savings are split by severity (using default proportions) and converted to 2002 monetary values, based on the following average (default) casualty costs:
♦ fatal - £1,249,890;
♦ serious - £140,450;
♦ slight - £10,830.
STOKE GIFFORD BYPASS STUDY Policy Review and Scheme Appraisal
SUMMARY OF ACCIDENT BENEFITS 5.32 The results of the COBA accident analysis are summarised in Table 5.3. The
table shows that the Stoke Gifford bypass would increase the number of personal injury accidents within the study area (shown in Figure 5.1) by between 180 and 290 over the 60 year appraisal period. This would increase accident costs by between £5.8 and £8.9 million.
Notes: 1. Accident savings calculated by COBA for the study area shown in Figure 5.1
2. Based on a 60 year appraisal period (2016–2075)
3. Accident costs and benefits are in constant 2002 prices, discounted to 2002 at 3.5% per annum (for the first 30 years) and 3.0% (thereafter).
5.33 Although the bypass would be built to high standards and would itself be expected to exhibit a relatively low accident rate, the increase in vehicle-kilometres caused by the scheme would have an adverse impact over the wider network.
SUMMARY OF THE ECONOMIC APPRAISAL 5.34 The results of the economic appraisal are presented in Table 5.4. All costs
and benefits are expressed in 2002 prices.
5.35 The costs of constructing the scheme, including land and property costs, preparation, supervision, and allowances for contingencies and optimism bias, have been estimated at £17.6 million for the Purple and Blue Routes, and £20.3 million for the Pink and Turquoise options, at current (2006) prices. Table 5.4 shows that the discounted cost of this investment would be £10.9 and 12.5 million respectively.
5.36 The appraisal also includes the costs to central government, in the form of lost revenues from indirect taxation.
STOKE GIFFORD BYPASS STUDY Policy Review and Scheme Appraisal
5.37 The total present value of the transport economic efficiency benefits, excluding accident savings, is estimated to be between £461 million and £663 million. Given the extent of the modelled network and levels of congestion in the forecast networks, some spurious benefits from outside the local area could be included in these estimates. Sector analysis has suggested that these could be 40% or more of the total benefits. On the other hand, the current appraisal takes account of benefits accrued during the AM peak and inter-peak periods only, and excludes potential benefits in other time periods.
5.38 Accident costs have been estimated using the DfT’s COBA program. On this basis, the number of personal injury accidents in the local area would increase as a result of the scheme, by up to 1.5% over the 60 year appraisal period. This reflects an increase in vehicle-kilometres travelled by drivers accessing the bypass. The present value of these additional accident costs, which represent a disbenefit to the scheme, is estimated to be between £5.8 million and £8.9 million.
5.39 The Benefit/Cost Ratio (BCR) varies between 23 and 31. On this basis, the Stoke Gifford bypass would offer very good value for money.
5.40 At a meeting of 21 March 2006 to discuss the preliminary findings of the study, members expressed concern that the Scenario F land-use assumptions included housing development at Earthcott, to the north of the M4. Sensitivity tests have therefore been undertaken on the Purple Route option in order to determine the potential impact of the site on scheme benefits.
5.41 These tests, which removed trips generated by the proposed housing from the forecast trip matrices without relocating them elsewhere, showed that the BCR (excluding accident benefits) would be reduced from 32 to 15 as a result. This is likely to represent a maximum impact given that the sensitivity test is based on smaller forecast trip matrices. If the housing development is removed from the trip matrices without any adjustment to the travel time and distance skims, the BCR would remain at 32.
STOKE GIFFORD BYPASS STUDY Policy Review and Scheme Appraisal
Central Government Funding - Indirect Tax Revenues 10,109 11,618 7,395 6,154
Total Present Value of Costs (PVC) 21,024 24,157 19,934 17,069
OVERALL IMPACT – INCLUDING ACCIDENT BENEFITS Total Present Value of TEE Benefits 662,818 618,951 461,742 462,121 Present Value of Accident Benefits -8,149 -7,876 -5,868 -8,842 Total Present Value of Benefits (PVB) 654,669 611,075 455,874 453,279 Total Present Value of Costs (PVC) 21,024 24,157 19,934 17,069
Net Present Value (NPV) 633,645 586,918 435,940 436,210 Benefit Cost Ratio (BCR) 31 25 23 27
Notes: 1. 60 year appraisal period: 2016 – 2075
2. All costs and benefits are at constant 2002 prices with future costs and benefits discounted to 2002 at 3.5% per annum
STOKE GIFFORD BYPASS STUDY Policy Review and Scheme Appraisal
6. Conclusions 6.1 Four route options have been considered for the Stoke Gifford Bypass.
Shown in Figure 3.2, the key features of the schemes are as follows:
♦ The Purple Route would take the more easterly of two alignments to the south of the railway line. It would have an at-grade crossing of Hambrook Lane, which is assumed to be a roundabout allowing all turning movements. Further south, it would have a roundabout junction with the access road to the Harry Stoke development, and would link to the more easterly of the two ARR junction locations;
♦ The Pink Route would take the more westerly of the two alignments, requiring an additional roundabout junction at the north end of the scheme, and would link to the more westerly of the two ARR junction locations. It would have a roundabout connection to Harry Stoke, but no connection with Hambrook Lane;
♦ The Turquoise Route would be similar to the Pink Route but would link to the more easterly ARR junction;
♦ The Blue Route would be similar to the Purple Route, but would have a signalised junction with Hambrook Lane, allowing straight-ahead movements only (i.e. no movements between the bypass and Hambrook Lane), and would link to the more westerly ARR junction.
6.2 These alternative schemes were coded into the test networks in detail, so that the model could simulate traffic movements through junctions and thus forecast their impacts on queues and delays. Roundabouts were assumed to be similar in dimension and capacity to those already in place on Great Stoke Way. The layout and signal timings for the proposed ARR junction were based on those already tested for the Greater Bristol Bus Network Major Scheme Bid (which included the junction to provide access for the Harry Stoke development).
6.3 Forecast AM peak and inter-peak traffic flows have been analysed for 2016 and 2031 for each scheme option so that the impacts of the bypass can be determined. Based on the traffic forecasts:
♦
♦
♦
The section of the Stoke Gifford bypass to the north of Hambrook Lane (where it crosses the railway line) would attract 2-way flows of between 1610 and 1970 vehicles per hour (vph) in the 2016 AM peak hour. Flows would be at the lower end of this range if turning movements were restricted at Hambrook Lane (as for the Blue option) or if no connection was made (as for the Pink and Turquoise options), and at the high end of the range if a full roundabout junction was provided (as for the Purple option). By 2031, traffic growth would have increased these peak hour flows to between 1750 vph and 2150 vph. Other sections of the bypass to the south of Hambrook Lane would attract lower peak hour flows, not exceeding 1760 vph by 2016 or 1900 vph by 2031. Inter-peak flows on all sections of the route would be significantly lower than peak hour flows, not exceeding 700 vph by 2016 or 925 vph by 2031.
STOKE GIFFORD BYPASS STUDY Policy Review and Scheme Appraisal
6.4 On this basis, a single carriageway road of 10 metre width would be adequate to accommodate forecast traffic demand to 2031. This would significantly reduce the cost of the scheme, assuming that SGC would not want to make provision for later construction of a Winterbourne bypass (Note: the scheme costs and modelling in this assessment have assumed a dual-carriageway bypass link).
6.5 Traffic attracted to the scheme would increase peak hour flows on southern sections of Bradley Stoke Way by 275-425 vph in 2016, and by 575-660 vph in 2031. Two way flows would then be about 1950 vph in 2031. Peak hour flows on northern sections of Bradley Stoke Way would be increased by about 250 vph in both 2016 and 2031.
6.6 Routes which run broadly parallel to the Stoke Gifford bypass, like Hatchett Road, Hambrook Lane, Westfield Lane, Brierly Furlong and Old Gloucester Road would generally be relieved by the scheme. This will provide an environmental improvement for residents, pedestrians and cyclists on these routes.
6.7 To the north and west, the bypass would attract additional traffic to routes like Bradley Stoke Way and Winterbourne Road. However, this would relieve other roads in the local area, notably Baileys Court Road, Orpheus Avenue and Braydon Avenue, i.e. through traffic is diverted to more appropriate routes. Some traffic would also be attracted from the A38.
6.8 Immediately to the west of the bypass, traffic flows on the A4174 Avon Ring Road would be reduced by up to 250 vph, some of which would transfer to Great Stoke Way and the Harry Stoke Link Road. Flows on the A38 to the north and south of the ARR would also be reduced.
6.9 To the south, the bypass would increase peak hour traffic flows on the A4174 ARR west of the M32 by up to 700 vph. This would have limited impact in 2016, and would in part be compensated by a reduction of 300 – 400 vph on the ARR to the east of the M32, which reflects a shift of traffic from the B4058 (Bristol Road and Winterbourne Hill) to the bypass. The M32 itself would be little affected by the scheme, since forecast traffic flows would be constrained by the available capacity whether or not the bypass scheme is implemented.
6.10 To the north and east of the bypass, High Street, Dragon Road and Down Road in Winterbourne would attract slightly higher traffic flows. However, this would be compensated by significant reductions in Hambrook Lane, Hicks Common Road, Winterbourne Hill and the B4058 Bristol Road. Flows on Beacon Lane would increase by over 100 vph. With the bypass in place, this route would carry more traffic to and from the north via High Street and less traffic to and from the south via Winterbourne Hill. This may place more stress on the Beacon Lane/High Street junction, but the reduction in through traffic, especially northbound on Winterbourne Hill may result in little net change in queue and delay at the junction. The A432 Badminton Road would be little affected by the scheme.
6.11 The model forecasts suggest that all four route options would have broadly similar impacts on traffic routing, and would help to relieve the centre of Stoke Gifford. There is little to choose between them in this respect. The forecasts also suggest that a junction with Hambrook Lane is unlikely to cause a major increase in rat-running.
STOKE GIFFORD BYPASS STUDY Policy Review and Scheme Appraisal
6.12 The results suggest that widespread traffic mitigation measures to manage changes in traffic routing are not required since traffic does appear to be routing along the main corridors and away from inappropriate residential routes. However this should be confirmed in future modelling analysis.
6.13 A comparison of bus journey times shows that the reduction in traffic flows and congestion on Hatchet Road and Brierly Furlong as a consequence of Stoke Gifford bypass generally reduces southbound bus journey times through the village in the AM peak hour by between one and three minutes (varying by bypass alignment option). Northbound bus journey time reductions are about one minute in this time period. Inter peak journey times are not affected as traffic flows are lower across the whole area. Similar reductions in journey times could be expected in the PM peak period, although this has not been modelled.
6.14 Traffic model results show that the proposed M4 widening between J19 and J20 would have little impact on traffic using the bypass, or on other roads in the Stoke Gifford local area.
6.15 Preliminary economic analysis of the scheme shows that it is likely to return a very good economic benefit. However further analysis is required to refine the benefit forecast by the modelling work to date.
STOKE GIFFORD BYPASS STUDY Policy Review and Scheme Appraisal