RPDMSuppVol3Part4B (2)

Road Planning and Design Manual Edition 2: Volume 3 Supplement to Austroads Guide to Road Design Part 4B: Roundabouts August 2014

Copyright

http://creativecommons.org/licenses/by/3.0/au/

© State of Queensland (Department of Transport and Main Roads) 2014

Feedback: Please send your feedback regarding this document to: [email protected]

Road Planning and Design Manual – Edition 2: Volume 3, Transport and Main Roads, August 2014

http://creativecommons.org/licenses/by/3.0/au/

mailto:[email protected]

Relationship with Austroads Guide to Road Design – Part 4B (2011)

The Department of Transport and Main Roads has, in principle, agreed to adopt the standards published in the Austroads Guide to Road Design (2011) Part 4B: Roundabouts.

When reference is made to other parts of the Austroads Guide to Road Design or the Austroads Guide to Traffic Management, the reader should also refer to Transport and Main Roads related manuals:

• Road Planning and Design Manual

• Traffic and Road Use Management Manual.

Where a section does not appear in the body of this supplement, the Austroads Guide to Road Design – Part 4B criteria is accepted unamended.

This supplement:

• has precedence over the Austroads Guide to Road Design – Part 4B when applied in Queensland

• details additional requirements, including accepted with amendments (additions or differences), new or not accepted

• has the same structure (section numbering, headings and contents) as Austroads Guide to Road Design – Part 4B.

The following table summarises the relationship between the Austroads Guide to Road Design – Part 4B and this supplement using the following criteria:

Accepted: Where a section does not appear in the body of this supplement, the Austroads Guide to Road Design – Part 4B is accepted.

Accepted with Amendments:

Part or all of the section has been accepted with additions and or differences.

New: There is no equivalent section in the Austroads Guide.

Not accepted: The section of the Austroads Guide is not accepted.

Austroads Guide to Road Design – Part 4B RPDM relationship

1 Introduction

1.1 Purpose Accepted

1.2 Scope of this part Accepted

1.3 Road safety Accepted

1.4 Road design objectives Accepted

1.5 Traffic management at roundabouts Accepted

1.6 Safety performance of roundabouts Accepted with amendments

1.7 Traffic capacity of roundabouts Accepted

1.8 Signalisation of roundabouts Accepted

1.9 Significant change from the guide to traffic engineering practice – part 6: roundabouts

Accepted

1.10 Roundabouts in high speed rural areas New

Road Planning and Design Manual – Edition 2: Volume 3, Transport and Main Roads, August 2014 i


2 Design principles and procedure

2.1 Terminology Accepted

2.2 Design principles Accepted

2.3 Design procedure Accepted with amendments

3 Sight distance

3.1 Introduction Accepted

3.2 Sight distance criteria Accepted

3.3 Truck stopping sight distance Accepted with amendments

4 Geometric design


4.2 Number of legs Accepted

4.3 Number of entry, circulating and exit lanes Accepted with amendments

4.4 Central island Accepted with amendments

4.5 Entry geometry Accepted with amendments 4.6 Circulating carriageway Accepted 4.7 Exit curves Accepted with amendments

4.8 Entry and exit widths Accepted

4.9 Separation between legs Accepted with amendments 4.10 Superelevation, gradient and drainage Accepted 4.11 Special treatments Accepted 5 Pedestrian and cyclist treatments


5.2 Pedestrians Accepted

5.3 Cyclists Accepted with amendments

6 Pavement markings and signing

6.1 Introduction Accepted with amendments

6.2 Single-lane local street roundabout Accepted

6.3 Multi-lane arterial road roundabout Accepted with amendments

7 Roadway lighting at roundabouts


7.2 Lighting consideration at roundabouts Accepted

7.3 Typical road lighting schemes at roundabouts Accepted

8 Landscaping and street furniture


8.2 Arterial road roundabouts Accepted

8.3 Local street roundabouts Accepted

8.4 Maintenance Accepted

References

References Accepted with amendments

Road Planning and Design Manual – Edition 2: Volume 3, Transport and Main Roads, August 2014 ii


Appendices

Appendix A Crash types Accepted

Appendix B Roundabout study and program Accepted

Appendix C Methods of improving roundabout entries Accepted

Appendix D Linemarking of multi-lane roundabouts Accepted

Appendix E Extended Design Domain (EDD) for entry path radii New

Commentaries

Commentary 1 Accepted



Road Planning and Design Manual – Edition 2: Volume 3, Transport and Main Roads, August 2014 iii

Contents

1 Introduction ....................................................................................................................................1

1.6 Safety performance of roundabouts ............................................................................................... 1

1.10 Roundabouts in high speed rural areas .......................................................................................... 1

2 Design principles and procedure .................................................................................................1

2.3 Design procedure ........................................................................................................................... 1

3 Sight distance ................................................................................................................................2

3.3 Truck stopping sight distance ......................................................................................................... 2

4 Geometric design...........................................................................................................................2 4.3.1 Introduction .....................................................................................................................2 4.4.3 Central island radius .......................................................................................................2 4.5.2 Single entry curve approach ...........................................................................................3 4.5.3 Reverse curves on approaches ......................................................................................3 4.5.5 Maximum entry path radius ............................................................................................4

4.7 Exit curves ...................................................................................................................................... 5

4.9 Separation between legs ................................................................................................................ 5

5 Pedestrian and cyclist treatments ...............................................................................................7 5.3.4 Multi-lane roundabouts on arterial roads ........................................................................7

6 Pavement markings and signing ..................................................................................................7

6.1 Introduction ..................................................................................................................................... 7

6.3 Multi-lane arterial roundabout ......................................................................................................... 7

References ..............................................................................................................................................8

Appendix E – Extended Design Domain (EDD) for entry path radii ..................................................9

Tables

Table 4B-1 – Guide for selecting the initial central island radius for a circular roundabout .................... 3

Table 4B-2 – Maximum entry path radii for one and two-lane roundabouts ........................................... 4

Table 4B-E 1 – EDD maximum entry path radii for one and two-lane roundabouts ............................... 9

Figures

Figure 4B-1 – Examples showing desirable and undesirable separation between roundabout legs on multilane roundabouts ............................................................................................................................. 6

Figure 4B-2 – Splitter kerb on roundabout approach separating cyclists from adjacent lanes ............... 7

Road Planning and Design Manual – Edition 2: Volume 3, Transport and Main Roads, August 2014 iv

Supplement to Austroads Guide to Road Design Part 4B: Roundabouts

1 Introduction

1.6 Safety performance of roundabouts

Additions

Motorcyclists are overrepresented in crashes at roundabouts. Additional issues to be considered for roundabouts include:

• recognition of the roundabout – design should ensure an early appreciation of the situation

• visibility of the central island, particularly at night

• visibility of splitter islands

• motorcyclist frangible signage

• line marking – materials should have a skid resistance similar to that of the road surface, and

• sight lines to motorcycles and sight lines of motorcyclists should not be blocked by landscaping, signage or island treatments.

Speed has been identified as a major contributing factor to the occurrence and severity of many crashes at intersections, including roundabouts. At rural intersections this factor is exacerbated due to the high speed differential between conflicting movements. Austroads (2014) describes methods for reducing speeds on rural roads and includes a range of treatments for application at rural roundabouts.

1.10 Roundabouts in high speed rural areas

There is no equivalent Section 1.10 in Austroads Guide to Road Design – Part 4B.

New

Austroads (2010a) and (2009) discusses the crash benefit of installing roundabouts at rural cross intersections (including those in areas with high desired speeds) at which there is an accident problem involving crossing or right-turn (versus opposing) traffic. This treatment is cited as achieving an expected reduction of 70% in adjacent approach crashes but with an increase of 20% in lower severity rear-end crashes. However, if the traffic flow on the lower volume road is less than about 200 vehicles per day, consideration could be given to using a staggered “T” treatment.

2 Design principles and procedure

2.3 Design procedure

Differences

Table 2.1 – Replace the text in the Consideration column for Step 8 as follows:

For single-lane and two-lane circular roundabouts, the Transport and Main Roads ARNDT roundabout program is preferred. It has the advantage of checking all the roundabout safety parameters listed in Arndt (1998) and is a more complete design check. Ensure that all of the limits of the roundabout safety parameters in ARNDT are not exceeded.

Alternatively, draw entry path radii in accordance with Section 4.5.5. If an entry path radius is greater than that shown in Table 4.2, an alternative geometric layout should be trialled.

Road Planning and Design Manual – Edition 2: Volume 3, Transport and Main Roads, August 2014 1


3 Sight distance

3.3 Truck stopping sight distance

Additions

Roundabouts should also cater for truck sight distance as follows:

• Criterion 1 sight distance – ensure that truck approach sight distance is provided to the roundabout from each leg, measured from a 2.4 m eye height to a 0 m object height (refer Section 3.2.1).

• Criterion 2 sight distance – ensure that a truck driver with a 2.4 m eye height at location ‘A’ on Figure 3.1 has sufficient sight distance according to the criteria in Section 3.2.2.

• Criterion 3 sight distance – ensure that a truck driver approaching the roundabout with a 2.4 m eye height can see other entering vehicles before the truck driver reaches the holding line, according to the criteria in Section 3.2.3.

4 Geometric design

4.3.1 Introduction

Additions

Two-lane roundabouts on single carriageway roads can promote overtaking within the roundabout, especially if there are no overtaking opportunities in close proximity on the upstream side of the roundabout. This situation causes driver frustration and is often the topic of complaints by motorists (including heavy vehicle operators). This situation should be avoided where possible by:

• providing a single-lane roundabout for as long as possible until traffic volumes warrant the use of a dual-lane facility, or

• providing one lane only for the through movement, subject to traffic volumes, and/or

• providing overtaking lanes prior to the approach.

4.4.3 Central island radius

Differences

The word “Minimum” is deleted from the title of this section to read “Central Island Radius”.

Table 4.1 in Austroads Guide to Road Design – Part 4B is replaced with Table 4B-1. The word “minimum” is deleted from the title and first row of the table headings. The word “absolute” in the table sub-heading is replaced with the word “minimum”. Notes to the table are amended.

The 3rd and 4th paragraphs in this section of Austroads Guide to Road Design – Part 4B are replaced with the following:

Table 4B-1 is a guide for the selection of the central island radius for a circular roundabout. The desirable central island radius provides an optimum safety outcome. Central islands larger than the desirable radius can result in increased circulating speeds and increased conflict between circulating and exiting traffic (refer section 4.9). However they also provide greater opportunity to provide entry curve geometry and to address other conditions as described later in section 4.4.3 of Austroads Guide to Road Design – Part 4B.

The criteria in the table should enable acceptable entry geometry in accordance with Table 4.2 of Austroads Guide to Road Design – Part 4B to be provided on each leg (Arndt 2008). The desirable



values given in Table 4B-1 should be used as a starting point whenever possible as they generally produce lower overall crash rates than those produced by the minimum values (Notes 2 and 3 in Table 4B-1).

Table 4B-1 – Guide for selecting the initial central island radius for a circular roundabout

Desired driver speed

on the fastest leg prior to the roundabout

(km/h)

Central island radius of a single-lane

roundabout (m)

Central island radius of a two-lane roundabout

(m) Speed reduction treatments required

prior to the entry curve(1) Minimum(5) Desirable Minimum(5) Desirable

≤ 40(2) 5(4) 10 8 12 No

50(2) 8 11 8 12 No

60(3) 10 12 14 16 No

70(3) 12 18 18 20 No

80(3) 14 22 20 24 Desirably

≥ 90(3) 14 22 20 24 Yes Notes:

1. Refer to Section 4.5.2 of Austroads Guide to Road Resign – Part 4B for the various types of speed reduction treatments

2. The desirable central island radii listed for these speeds generally provide sufficient size splitter islands for storage of pedestrians combined with desirable entry curvature. The minimum central island radii generally do not. In addition, the desirable values will generally produce a lower overall crash rate than what the minimum values will.

3. The desirable central island radii listed for these speeds provide a maximum decrease in speed between the entry curve and a right-turn on the circulating carriageway of 20 km/h. This minimises the number of potential single vehicle crashes on the circulating carriageway. The minimum central island radii are associated with values up to 30 km/h. In addition, the desirable values will generally produce lower overall crash rates than what the absolute values will.

4. Minimum central island radius where the design right-turn vehicle is a single unit truck is 7 m.

5. The minimum central island radii should typically only be selected for an initial central island radius in constrained brownfield sites. Selection of these radii may lead to some geometric design elements not complying with Normal Design Domain criteria.

4.5.2 Single entry curve approach

Additions

If using short horizontal straights between entry and circulating carriageway curves, a length of 5 m is usually sufficient to accommodate heavy vehicle dynamics. It is recommended that the design of roundabouts on departmental roadways incorporate these short horizontal straights. To model a roundabout incorporating short horizontal straights with the Transport and Main Roads ARNDT program, leave out the straights.

4.5.3 Reverse curves on approaches

Additions

Any vertical curve used in conjunction with an approach curve will result in a lower perception of downstream approach curves and/or entry curve, particularly if used in combination with



superelevation. If a vertical curve cannot be avoided, it may be best to use an alternative treatment (refer latter section) rather than reverse approach curves. This principle is the same as that used on a midblock section of roadway, i.e. a crest curve should never be provided immediately prior to a tight horizontal curve.

The reverse curve treatment should desirably be provided with adequate superelevation (of 2.5% to 3% on each of the curves to aid heavy vehicle stability) in combination with short horizontal straights (see below). However, applying superelevation on reverse approach curves may produce poor perception of downstream horizontal curves (including other approach curves and the entry curve). An alternative is to use adverse crossfall on one (or more) of the reverse approach curves and keep the crossfall within the same direction through the approach curves and entry curve.

The design of the superelevation through the reverse curves may involve:

• Use of short horizontal straights between each curve (desirable) in order to obtain the required superelevation on each curve, to reduce sudden steering movements and to provide more time for drivers to react to each successive curve. Typically, this case is covered by cases 3B, 4A and 4B given in Appendix E of Austroads Guide to Road Design – Part 3: Geometric Design (Austroads 2010). To model a roundabout incorporating short horizontal straights with the ARNDT program, leave out the straights.

• Transition of superelevation within reverse circular curves (in constrained situations) where it is not possible to incorporate short horizontal straights. Typically, this case is covered by cases 3A and 3B given in Appendix E of Austroads Guide to Road Design – Part 3. However, such treatment may reduce the stability of heavy vehicles. Consider using alternative treatments to the use of reverse curves in this case.

The alternative treatments (as listed in section 4.5.3 of Austroads Guide to Road Design – Part 4B), to the use of reverse curves to create a lower desired speed on the approach, should be considered as equal alternatives to reverse curves.

4.5.5 Maximum entry path radius

Differences

Table 4.2 in Austroads Guide to Road Design – Part 4B is replaced with Table 4B-2.

Table 4B-2 – Maximum entry path radii for one and two-lane roundabouts


on the leg prior to the roundabout

(km/h)

Maximum entry path radius (m)(5)

Single-lane entries(1)

Two-lane entry – staying in correct

lane(2)

Two-lane entry – cutting across lanes(3)

≤ 40

55

1.9 x actual entry path radius when staying in correct lane(4)

50 1.8 x actual entry path radius when staying in correct lane(4)




≥ 90 1.5 x actual entry path radius when staying in correct lane(4)



Notes:

1. Construction of the entry path of a single-lane entry for roundabouts comprising one or two circulating lanes is given in Figure 4.6 of Austroads Guide to Road Design – Part 4B.

2. Construction of the entry path of a two-lane entry - staying in the correct lane for a two-lane roundabout is given in Figure 4.7 of Austroads Guide to Road Design – Part 4B.

3. Construction of the entry path of a two-lane entry - cutting across lanes for a two-lane roundabout is given in Figure 4.8 of Austroads Guide to Road Design – Part 4B.

4. Radius of the entry path for drivers staying in the correct lane as determined in Figure 4.7 of Austroads Guide to Road Design – Part 4B.

5. EDD values for the design of the entry path radii for one and two-lane roundabouts are provided in Appendix E.

The 5th paragraph in this section of Austroads Guide to Road Design – Part 4B is replaced with the following:

For single-lane and two-lane circular roundabouts, it is preferred that the designer use the ARNDT roundabout program instead of the manual method given in this section of Austroads Guide to Road Design – Part 4B. Ensure that all of the limits of the roundabout safety parameters in ARNDT are not exceeded. The ARNDT program has the advantage of checking all the roundabout safety parameters listed in Arndt (1998) and is therefore a more thorough design check.

For all other types of roundabouts, use the manual method given in this section of Austroads Guide to Road Design – Part 4B.

4.7 Exit curves

Additions

If using short horizontal straights between circulating carriageway and exit curves, a length of 5 m is usually sufficient to accommodate heavy vehicle dynamics. It is recommended that the design of roundabouts on departmental roadways incorporate these short horizontal straights. To model a roundabout incorporating short horizontal straights with the ARNDT program, leave out the straights.

4.9 Separation between legs

Additions

Additional conflicts can occur at two-lane roundabouts with the following geometry at a roundabout entry:

• two circulating lanes where a two-lane entrance is followed by a two-lane exit

• a significant distance between the two-lane entry and the next downstream exit

• both circulating lanes marked allowing departure at the next exit

• both entry lanes marked allowing circulation past the next roundabout exit.

In the first diagram in Figure 4B-1, an entering vehicle in the left lane, travelling around the roundabout, immediately crosses the exiting lanes after entering the roundabout. In the second diagram in Figure 4B-1, an entering vehicle in the left lane, travelling around the roundabout, travels parallel to the inside lane for some distance. The entering vehicle then has to cross the exit path at the first downstream exit of a vehicle in the inner lane. In this circumstance there is an increased potential for conflict between the entering vehicle and a circulating vehicle departing at the next exit and an increase in exiting/circulating vehicle accidents is likely to occur. It is strongly recommended that roundabout geometry shown in the second diagram of Figure 4B-1 not be accepted.



Figure 4B-1 – Examples showing desirable and undesirable separation between roundabout legs on multilane roundabouts

Note:

The linemarking in the second diagram is shown for clarity purposes only. In practice, this linemarking would require a vehicle entering in the left lane to exit at the next exit which is in conflict with the approach pavement arrows.



5 Pedestrian and cyclist treatments

5.3.4 Multi-lane roundabouts on arterial roads

Additions

Figure 4B-2 shows a Queensland example of an island separating cyclists from motor vehicles.

Figure 4B-2 – Splitter kerb on roundabout approach separating cyclists from adjacent lanes

Note:

The treatment shown in this figure can have durability problems with vehicle impacts on the island, particularly the leading unit bending the pavement bolts, resulting in the rubber kerb becoming free and hazardous. The leading edge of the kerb should therefore be a keyed-in concrete version.

6 Pavement markings and signing

6.1 Introduction

Additions

Wherever a reference to AS 1742.2 – Manual of Uniform Traffic Control Devices occurs, the Transport and Main Roads Manual of Uniform Traffic Control Devices must be used.

6.3 Multi-lane arterial roundabout

Difference

Replace the last paragraph in this section with the following:

In special circumstances, a spiral marking treatment at multi-lane roundabouts may be required, e.g. to provide two-lane capacity from an entry leg to an exit beyond the second exit leg. Spiral line marking may lead to increased driver workload and confusion and signage currently does not exist to adequately show the correct lane usage through the roundabout for particular movements. For this reason, it is desirable that spiral line-marking not be used for the design of roundabouts in greenfield sites. Instead, spiral line-marking should generally be considered only as a solution to minimising operational problems on existing roundabouts where no other solution is feasible. Refer to Appendix D of Austroads Guide to Road Design – Part 4B for further discussion on this topic.



References

Transport and Main Roads publication references refer to the latest published document on the departmental website (www.tmr.qld.gov.au).

Additions

Austroads (2009) Guide to Road Safety Part 8: Treatment of Crash Locations, Austroads, Sydney, NSW

Austroads (2010) Guide to Road Design Part 3, Geometric Design, Austroads, Sydney, NSW

Austroads (2010a) Austroads Technical Report – Road Safety Engineering Risk Assessment Part 9: Rural Intersection Crashes, Austroads, Sydney, NSW

Austroads (2011) Guide to Road Design Part 4B, Roundabouts, Austroads, Sydney, NSW

Austroads (2014) Methods for Reducing Speeds on Rural Roads – Compendium of Good Practice, AP-R449-14, Austroads, Sydney, NSW

Transport and Main Roads ARNDT software program, Transport and Main Roads, Brisbane, QLD

Transport and Main Roads Manual of Uniform Traffic Control Devices, Brisbane, QLD


http://www.tmr.qld.gov.au/


Appendix E – Extended Design Domain (EDD) for entry path radii

There is no equivalent Appendix E in Austroads Guide to Road Design – Part 4B.

New

The maximum entry path radii in Section 4.5.5 are based on achieving a desired maximum entry speed for vehicles which will generally minimise crash rates. The following entry path radii are larger than those in Section 4.5.5 and may be acceptable to use where existing site constraints result in adoption of the NDD values being unachievable.

Table 4B-E 1 – EDD maximum entry path radii for one and two-lane roundabouts


on the leg prior to the roundabout

(km/h)

Maximum entry path radius (m)

Single-lane entries(1) Two-lane entry –

staying in correct lane(2) Two-lane entry – cutting across lanes(3)

≤ 40 100 1.9 x actual entry path radius when staying in correct lane(4)

50 80 1.8 x actual entry path radius when staying in correct lane(4)




≥ 90 55 1.5 x actual entry path radius when staying in correct lane(4)

Notes:

1. Construction of the entry path of a single-lane entry for roundabouts comprising one or two circulating lanes is given in Figure 4.6 of Austroads Guide to Road Design – Part 4B.

2. Construction of the entry path of a two-lane entry – staying in the correct lane for a two-lane roundabout is given in Figure 4.7 of Austroads Guide to Road Design – Part 4B.

3. Construction of the entry path of a two-lane entry - cutting across lanes for a two-lane roundabout is given in Figure 4.8 of Austroads Guide to Road Design – Part 4B.

4. Radius of the entry path for drivers staying in the correct lane as determined in Figure 4.7 of Austroads Guide to Road Design – Part 4B.


RPDMSuppVol3Part4B (2)

Documents

austroads guide

road design objectives

design procedure

design principles

geometric design

design manual traffic

road safety

design manual edition