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This publication is available at https://www.gov.uk/government/consultations/air-quality-brake-tyre-and-road-surface-wear-call-for-evidence/outcome/brake-tyre-and-road-surface-wear-call-for-evidence-summary-of-responses
1.1) Air pollution is a major public health risk ranking alongside cancer, heart disease and obesity, and poses the single greatest environmental risk to human health. As well as human health, air pollution also has implications for the natural environment and for the economy. The government is fully committed to tackling air pollution and has put in place a £3.5 billion plan to reach compliance with legal limits for nitrogen dioxide, by reducing exhaust emissions from road transport.
1.2) The UK also has ambitious, international targets in place to significantly reduce emissions of five damaging air pollutants by 2020 and 2030. We have published a world leading Clean Air Strategy in January 2019 which sets out the actions we will take to meet these targets and for particulate matter (PM) goes beyond the EU requirements by committing to setting a new, ambitious, long-term target to reduce public exposure to PM concentrations above WHO guidelines.
1.3) Vehicle non-exhaust PM is emitted from the use of brakes and friction between tyres and road surfaces, so is a result of essential vehicle safety systems. Increasingly stringent ’Euro Standards’ legislation to reduce exhaust emissions from road transport have been very successful in addressing exhaust PM, to the point that it is already estimated to be a smaller source than non-exhaust PM and expected to be less than 10% of total road transport PM by 2030. As other emission sources of PM are addressed, it is estimated that the non-exhaust component will increase in importance, growing from less than 8% of national emissions in 2017 to 10% in 2030.
1.4) Recognising the impact of PM on human health, and the growing importance of non-exhaust PM, government held a call for evidence on this issue (which closed on 28 September 2018).
1.5) This document summarises the evidence received and sets out how it will be used to inform policy development. The government is grateful to all those who contributed to the call for evidence.
2. Summary of responses
2.1) The consultation received 54 responses, 14 from individuals and 40 from organisations representing business, public bodies and academia.
2.2) A large number of responses were qualitative in nature and there was a limited amount of new evidence provided; some responses signposted to publications and studies that Defra, DfT and/or the Air Quality Expert Group were already aware of. Only a few responses offered novel evidence in support of the positions stated.
Evidence: brake and tyre wear
2.3) In the UK, emissions from brake and tyre wear are estimated using the methodology of 2016 European Monitoring and Evaluation Programme/European Environment Agency (EMEP/EEA) Guidebook combining emission factors in milligrams emitted per kilometre (mg/km) by class of vehicle and vehicle kilometres travelled per year as set out in the Call for Evidence document.
2.4) Respondents provided emission factors for PM10 emissions from conventional passenger vehicles in the rage of 2 – 13 mg/km but noted that the data was not comparable across vehicle classes as emissions vary hugely as a function of weight; no data were submitted for other vehicle classes.
2.5) It was noted that the contribution from emissions from brake and tyre wear to air pollution can be assessed by combining knowledge of atmospheric chemistry and the using suitable tracer chemicals (such as barium, copper, iron and antimony) to isolate and identify emissions – indeed a standardised ISO/TS 20593:2017 method exists for measurement of tyre and road wear PM in ambient air samples.
2.6) Suggestions for the improvement of brake wear measurements focused on the test procedure being developed by the UNECE United Nations Economic Commission for Europe (UNECE) Particle Measurement Programme Informal Working Group (PMP IWG). As regards tyre wear, the key development mentioned by respondents was the European Commission (EC) proposal that an experimental method for measurement of tyre abrasion should be developed as part of the tyre labelling regulations. Some respondents suggested the use of proxy methods for measuring particle emissions such as MOT data, vehicle service records and tyre and brake sale records.
2.7) Respondents acknowledged that there are no robust, publically available data on brake wear from electrical vehicles (EVs) or those with regenerative braking, but anecdotal evidence suggested there would be a reduction in emissions where regenerative braking is used. Without regenerative braking, emissions were expected to increase due to the increase in vehicle weight.
2.8) Data on tyre wear from EVs was also noted to be lacking or not publically available. Nonetheless, many of the respondents assumed that increased EV weight would lead to increased tyre wear, and possibly higher ultrafine particulate emissions, although no data was submitted to support this.
2.9) Some respondents noted that despite the potential for increased brake and tyre wear in EVs, technological improvements and changes in driving style and weight reduction measures could be mitigating factors.
2.9) As regards the uptake of electric vehicles with one pedal driving technology (whereby regenerative braking is provided as soon as the driver lifts off the accelerator), the following suggestions were received for factors that could increase their uptake: knowledge of their increased efficiency (and battery range) and that they are safer and potentially less polluting than conventional fuel cars. One major barrier noted was the higher up-front cost and the fact that cost savings would not be realised immediately.
2.10) Emerging technologies such as novel brake pad and rotor lining materials were noted for their potential role in reducing emissions from brake and tyre wear. As well as regenerative and electrical braking, the use of engine braking, regenerative and electrical braking were also suggested. For tyres, use of less harmful substances in manufacturing and increased use of tyre pressure monitoring systems were suggested to reduce emissions and their impacts. Emission capture options were also suggested for brakes.
2.11) Legislation was suggested as a key factor which would increase the uptake of emerging technology for reducing brake and tyre wear emissions. Regulation (EC) 661/2009 of the European Parliament that mandates the installation of tyre pressure monitoring systems in all vehicles post 2014 was cited. Furthermore, it was noted that premium car makers had more incentive to reduce emissions for aesthetic reasons (to avoid black marks on wheel rims). Finally, funding and financial incentives and published emission scoring labels on tyres were noted as motivating factors.
Evidence: road abrasion
2.12) Particle emissions from road abrasion are also estimated in mg/km using the methodology of the EMEP/EEA guidebook, yet respondents noted there are large uncertainties since factors such road topography (whether a road is hilly or winding as opposed to a gently inclined straight road), road surface condition, age, features (such as traffic calming measures) and vehicle speed all affect road abrasion.
2.13) A majority of respondents identified road surface material and features as having an impact on emissions from road abrasion but no firm evidence was provided. Traffic calming measures attracted particular attention, with many respondents suggesting that badly designed speed bumps resulted in increased emissions and that the frequent braking and acceleration resulted in higher tyre wear and brake particle emissions. Some respondents also suggested that road maintenance methods could be improved to reduce particle emissions.
2.14) Road topography, weather conditions and road surface temperature were noted as further factors influencing particulate emission from road abrasion.
2.15) As regards road surface condition and ageing, some respondents stated that older roads would contribute more particulate emissions, but without providing data to back this claim. Additionally, pot-holes were mentioned as a contributing factor to road surface abrasion and tyre wear.
2.16) A few respondents noted that using recycled plastic or tyre chips to replace a fraction of the bitumen in the asphalt mix could impact on emissions from road surface abrasion.
2.17) Some noted that when studying the chemical composition of particles from road abrasion it was often difficult to distinguish with certainty between particles from road abrasion and other particles deposited on the road surface with similar composition.
Evidence: Impacts of tyre and road marking wear on the marine environment
2.18) The quantitative evidence submitted was hugely variable and inconsistent thus making a valid comparison or assessment difficult. A modelling study by the Norwegian Environment Agency was cited suggesting a large fraction of microplastic pollution in the Norwegian marine environment originated in from tyres. A respondent from industry cited figures derived from probabilistic modelling they had commissioned which estimated that only 2 – 5% of tyre and road wear particles end up in estuaries. Many respondents also noted the significance of the use of thermoplastics in road markings and the importance of finding alternatives.
2.19) A regulator stated that their work on a research project had shown evidence of polycyclic aromatic hydrocarbons (PAH), heavy metals and suspended solids (which includes PM from tyre and brake wear) from road run-off in sensitive groundwater areas, necessitating pollution mitigation measures such us Sustainable Urban Drainage Systems (SUDS), but did not provide any robust evidence.
2.20) Many respondents emphasised the importance of treating road surface run-off as a means of stopping the pathway of microplastics into the aquatic and marine environments using measures such as SUDS and hydrodynamic vortex separators. It was also noted that the risk assessment process for polycyclic aromatic hydrocarbons in highway outfall run-off should be improved as it was devised before the development of the present environmental and water quality standards for PAHs as set out in Annex II of Directive 2008/105/EC.
2.21) It was suggested that the majority of road run-off pollution in the aquatic environment took the form of a “shock load” and had potential to harm aquatic life and cause an impact in the food-chain, but no specific evidence was provided.
Policy options for reducing non-exhaust PM emissions
2.22) Several responses noted that a reduction in the number of vehicle journeys is a very effective means of pollution abatement without any other changes to brake and tyre technology, or driving behaviours. Shift to other modes of transport was suggested to reduce cars journeys. Key suggestions to promote shifts included promoting the use of public transport, the improvement of infrastructure to promote walking and cycling and improving legal frameworks protecting vulnerable road users from motorised traffic (such as cyclists).
2.23) Congestion reduction measures were a common response, such as congestion charging and smarter use of roads through active traffic management systems. Additionally, encouraging flexible working leading to journey time behaviour change, and better transport logistics to reduce the number of journeys, were proposed.
2.24) The promotion of better planning practices to reduce the number of journeys such as development where housing is built with recreational areas, amenities and employment within easy reach, was also suggested.
2.25) In the responses it was suggested that 30% of tyre wear could be attribute to driving style, so the promotion of better, smoother, more efficient driving styles by incorporating ‘eco’ driving into standard driver training and custom courses could be a good means of reducing non-exhaust and other emissions. Similarly, respondents suggested emission reductions could be achieved by using smaller, lighter vehicles where possible to perform the same function.
2.26) Technical improvements to road design through better, novel materials and maintenance regimes, in addition to the reduction of unnecessary road repair, use of lower emission road resurfacing techniques, were proposed.
2.27) Some respondents suggested that where technical solutions for emission reduction are developed, the government can play a role their uptake.
2.29) A few responses noted the importance of focusing on health and epidemiological studies such as correlating respiratory health with proximity to major roads, studying brake particle deposition on lung cells, characterising exposure of communities living near roadways, researching the impact of carbon fibre and carbon nanotubes emitted from brake shoes and pads.
2.30) Some responses suggested the importance of understanding and reducing water pollution from brake and tyre wear and improving the monitoring of waterways for compounds from road surface run-off such as polycyclic aromatic hydrocarbons (PAHs).
2.31) A few responses noted the importance of considering historic vehicles and materials in older vehicles, querying whether asbestos is still present in older vehicle brake pads; while one respondent argued for the exemption of historic vehicles from any stringent regulations until suitable alternative tyre and brake materials could be found for these vehicle with cultural heritage significance.
3.1) The government is grateful to all those who took the time to contribute to the call for evidence, both formally through written responses and during discussions with officials.
3.2) The responses received suggested that there are a range of technologies and approaches which may be able to deliver reductions in PM emissions, such as driving style, alternative materials for brakes, tyres and roads, or regenerative braking, but did not supply data quantifying their effectiveness or combined effects. Responses noted the lack of internationally agreed measurement methods, and that the emission factors currently used to estimate national emissions from these sources may have become dated as technologies evolved.
3.3) Government is taking a leading role in addressing these emission sources. We commissioned a £200,000 research project to the University of Plymouth to assess the impact of microplastics from tyres and clothing on the marine environment, and have asked the Air Quality Expert Group to review the evidence on non-exhaust PM and make recommendations on how to address them, informed by the data submitted in this Call for Evidence. We will consider their conclusions and recommendations in deciding the next steps.
3.4) We will continue to engage at international level to take action on ocean microplastics, as well as to develop agreed methods for measuring non-exhaust emissions, as a means to assess the benefits of different technologies and to underpin the development of emission standards.
Annex A: Call for Evidence questions
1.1 Brake and tyre wear
Q1. Do you have any quantitative evidence for the level of emissions which come from brake and tyre wear? We would welcome evidence on emissions from different vehicle classes and different types of tyres and brakes, and on different road surfaces.
Q2. Do you know of a better, more reliable way to calculate the emissions from brake and tyre wear?
Q3. Do you have data of PM emissions from braking in electric or hybrid vehicles, and/or a comparison with brake emissions from conventionally fuelled vehicles?
Q4. Do have data on PM emissions from tyre wear of electric or hybrid vehicles, and/or a comparison with tyre wear emissions from conventionally fuelled vehicles?
Q5. What might encourage drivers to buy a car which has “one pedal driving” technology fitted, and maximise regenerative braking?
Q6. Do you have any suggestions for how PM emissions from brakes and tyres should be tested? Or how a suitable test method could be developed? Please provide reasons for choosing your preferred testing method.
Q7. Are you aware of any new or emerging technologies or materials which could reduce the emissions from brake and tyre wear?
Q8. If so, what, if anything, could speed up the development and/or uptake of these technologies?
1.2 Road abrasion
Q9. Do you have evidence for the contribution of road abrasion to particulate emissions?
Q10. Do you have evidence of how changes in road surface material influence the level of PM emissions from road traffic?
Q11. Do you have evidence of the impact of ageing/deterioration of the road surface on PM emissions?
Q12. What other factors might influence the extent of PM emissions from road abrasion? Do you have any evidence of their effect?
1.3 Impacts of tyre and road marking wear on the marine environment
Q 13. Do you have any evidence for the presence, extent and environmental impact of micro-plastic particles from these sources? We would also be interested to receive evidence of the pathways by which they reach the marine environment.
2. Policy options for reducing non-exhaust PM emissions
Q14. Do you have any views on the options identified [in the Call for Evidence] for reducing non-exhaust PM emissions, or other suggestions of measures that could be taken to reduce non-exhaust PM emissions and their impact on air quality? Please justify your views.
Q15. We know that the way in which a vehicle is driven (such as degree of acceleration, braking and overall anticipation) and generally managed (such as avoiding carrying unnecessary weight) can affect the level of emissions. Do you have evidence of the impact of different driving styles or of the other options identified above or in your response to Q13 on emissions of PM from brake, tyre and road wear?
3. Additional evidence
Q16. Are there any issues not covered in previous questions where you would like to provide evidence, such as on the health or environmental impacts of PM emissions from brake, tyre and road wear?
Annex B: Respondents
We have received 54 responses, 14 from individuals and 40 from organisations representing business, public bodies and academia, including:
Aquality Trading & Consulting Ltd
Auto Industry Consulting Ltd
Centre for London
Environmental Protection Scotland
ETRMA - European Tyre & Rubber Manufacturers’ Association
European Commission’s Joint Research Centre
Freight Transport Association
Hertfordshire County Council
Japan Automobile Research Institute (JARI)
Light Rail (UK)
Mineral Products Association
Road Haulage Association
Steertrak UK Ltd
Student Open Universiteit
The Heritage Alliance
The Society of Motor Manufacturers and Traders Limited
The university of Birmingham
Transport for London
UK Health Alliance on Climate Change
UK Petroleum Industry Association
United States Environmental Protection Agency
University of Cambridge
Waltham Forest London Borough
ZF Active and Passive Safety Technology