Mitigation Options for Motorways A review of the literature Roger Barrowcliffe and Michael Bull 1.

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Mitigation Options for Motorways

A review of the literatureRoger Barrowcliffe and Michael Bull

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Context Defining the problem Sources of information Source – pathway – receptor Conclusions

Content

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Pressure to enhance motorway network by increasing capacity

Some schemes are unable to proceed because of their implications for air quality and compliance with limit values, chiefly NO2.

In the absence of any control over the vehicle types using the motorway, what are the alternative means of reducing air quality impacts?

Context

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Defining the problem

M25, Essex70 mph speed cars, 60 mph HGVs

2013 EFT

100.000 veh/day

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Looking Ahead

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Consult with: Government departments, local government, government agencies, academics and European research organisations.

Search scientific and grey literature, eg the Dutch Innovatieprogramma Luchtwaliteit or IPL

Analyse and evaluate findings Produce a draft report

What we did

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Purchase properties? Not viable for a number of legal and ethical reasons

Modify properties? eg forced ventilation. Technically dubious and legally suspect. See planning inquiry decision on student accommodation near Blackwall Tunnel.)

Conclusion: little or no scope to solve problem by intervention at receptors.

Receptors

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Pathway modifications through: Barriers Enclosure in tunnels Pollutant removal by catalytic surfaces

Pathway

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Barriers – the theory

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Barriers – CFD modelling

Barrier No barrier

Notes: US EPA research

Bowker et al 2007

Birds eye view of a section of Interstate -440 in Raleigh, N Carolina

Complements field study

QUIC CFD model

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Barriers – road layout for this US EPA study

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Barriers – influence of buildings and trees

Observation:

The influence of obstacles behind the barrier dilutes its beneficial effect, in respect of pollutant concentrations

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Barriers – experimental data

Data from Dutch IPLField experiments at A28 siteMeasurements made of NOx, NO2

and PM10 over several months4m and 7 m noise barriers

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Barriers - A28 results for NOx

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Barriers – A28 result for NO2

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Catalytic surfaces using TiO2 for promoting oxidation to soluble nitrate.

Theoretical – no practical experimental evidence to support this technique in real world conditions.

Trials by HA alongside the M60 and also as part of the Dutch IPL.

Fails because of insufficient surface area, insufficient UV light, damp surfaces and insufficient pollutant contact with coated surface. 1% reduction at best.

Pollutant removal

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Enclosures

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A largely theoretical concept Investigated as part of the Dutch IPL Would almost eliminate motorway as a pollution

source along its length – although would concentrate pollution at tunnel portals.

Dutch IPL quotes costs of €6M -€65M per kilometre Passive pollutant removal possible through

catalytic coatings or pollutants dispersed as an elevated source through roof vents.

Enclosures -feasibility

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The Melbourne ‘Sound Tube’

Real world example built as a noise barrier

Melbourne CityLink urban freeway

300m long and costing AU$ 5 M

No reported data on air quality implications

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Influences on emissions: Traffic volumes Traffic composition, eg %age Euro VI/6 vehicles Flow state, ie free flow or congested

Emissions – speed reduction

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The most directly useful experience is that of Dutch urban motorways in the period 2002-2009.

80 kph speed limits imposed on 10 sections of motorway. Previous limits either 100 or 120 kph.

Extensive roadside measurements made of air pollutants, especially in Amsterdam. Coupled with dynamic emission simulation modelling (VISSIM).

Speed limit reduction – the evidence

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Speed limit trial results (Kalter et al 2005)

Location NOx emission

reduction

NOx

concentration decrease (road contribution)

NO2

concentration decrease (absolute)

A10 West 17% 12-20% 3-6%

A20 Rotterdam 9% 7-9% 1-3%

A13 Overschie 13% 10-14% 4-6%

A16 Dordrecht 8% 4-7% 0.5-2%

A12 Voorburg 11% 7-10% 2-3%

A9 Badhoeveddorp 19% 10-14% 1-2%

A12 Utrecht 17% 14-16% 4-5%

A2 Waardenburg 19% 10-16% 4-6%

A16 Rotterdam 9% 7-9% 1-2%

A4/A12 -zuid 15% 10-20% 3-5%

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The contribution of HGVs is important and influential in the outcome.

Positive outcomes arise through smoothing of flows.

Biggest improvements arise in PM concentrations, not NO2.

This intervention is politically charged and polarising.

The Dutch experience with speed limits – lessons learnt

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No easy solutions, but the HA is still committed to exploring options.

Effectiveness of the obvious interventions is limited – except for theoretical and expensive solutions such as enclosures or canopies.

Reducing emissions at source is ultimately the best solution – and will occur in time with the penetration of EuroVI/6 vehicles and the uptake of ultra low emission vehicles.

Closing thoughts