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

 Context  Defining the problem  Sources of information  Source – pathway – receptor  Conclusions 2 Content

 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 NO 2.  In the absence of any control over the vehicle types using the motorway, what are the alternative means of reducing air quality impacts? 3 Context

Defining the problem Clear Air Thinking4 M25, Essex 70 mph speed cars, 60 mph HGVs 2013 EFT veh/day

Looking Ahead 5

 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 Clear Air Thinking6 What we did

 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. Clear Air Thinking7 Receptors

 Pathway modifications through:  Barriers  Enclosure in tunnels  Pollutant removal by catalytic surfaces Clear Air Thinking8 Pathway

Barriers – the theory Clear Air Thinking9

Barriers – CFD modelling Clear Air Thinking10 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

Barriers – road layout for this US EPA study Clear Air Thinking11

Barriers – influence of buildings and trees Clear Air Thinking12 Observation: The influence of obstacles behind the barrier dilutes its beneficial effect, in respect of pollutant concentrations

Barriers – experimental data Clear Air Thinking13 Data from Dutch IPL Field experiments at A28 site Measurements made of NO x, NO 2 and PM 10 over several months 4m and 7 m noise barriers

Barriers - A28 results for NO x Clear Air Thinking14

Barriers – A28 result for NO 2 Clear Air Thinking15

 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. Clear Air Thinking16 Pollutant removal

Enclosures Clear Air Thinking17

 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. Clear Air Thinking18 Enclosures -feasibility

The Melbourne ‘Sound Tube’ Clear Air Thinking19 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

 Influences on emissions:  Traffic volumes  Traffic composition, eg %age Euro VI/6 vehicles  Flow state, ie free flow or congested Clear Air Thinking20 Emissions – speed reduction

 The most directly useful experience is that of Dutch urban motorways in the period  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). Clear Air Thinking21 Speed limit reduction – the evidence

Speed limit trial results (Kalter et al 2005) Clear Air Thinking22 Location NO x emission reduction NO x concentration decrease (road contribution) NO 2 concentration decrease (absolute) A10 West17%12-20%3-6% A20 Rotterdam9%7-9%1-3% A13 Overschie13%10-14%4-6% A16 Dordrecht8%4-7%0.5-2% A12 Voorburg11%7-10%2-3% A9 Badhoeveddorp19%10-14%1-2% A12 Utrecht17%14-16%4-5% A2 Waardenburg19%10-16%4-6% A16 Rotterdam9%7-9%1-2% A4/A12 -zuid15%10-20%3-5%

 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 NO 2.  This intervention is politically charged and polarising. Clear Air Thinking23 The Dutch experience with speed limits – lessons learnt

 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. 24 Closing thoughts