Each time a vehicle is driven, friction and the transfer of force between the tire and the road cause particles to be released from both the tire tread and the road surface. These are known as tire and road wear particles (TRWP) and are made up of approximately a half-and-half mixture of tire tread and road pavement materials.
Despite decades of academic and industry research, there is still a lot more work to be done to understand the real-world risks of TRWP. With growing environmental pressures and policy interest, the need to accelerate scientific knowledge is higher than ever. But this cannot be done in isolation — it demands harmonization: credible, collaborative research built on aligned approaches across various stakeholders.
The mandate for harmonization in TRWP science
The State of Knowledge (SOK) papers, supported by the Tire Industry Project (TIP), provide the most comprehensive review of tire wear emissions science to date, analyzing more than 850 peer-reviewed studies.
The SOK findings bring clarity to an extremely fragmented field. What exists today are different studies that define and measure tire wear emissions in different ways: some focus only on airborne particles, while others include particles deposited on road surfaces, soils, or transported into waterways. In addition, some studies also examine volatile and dissolved compounds released during tire use. Many of these use different definitions and measurement approaches that lead to widely varying estimates of tire wear emissions, making comparisons difficult.
The result is that numbers often vary dramatically – figures that make headlines but are difficult for regulators or the public to put in the right context. This in turn creates a risk that decisions could be made on incomplete or qualified data that is based on specific assumptions. Without harmonized methods and definitions, stakeholders could end up latching onto the biggest number, not the most reliable one.
This inconsistency isn’t limited to the quantum of wear emissions. Measurement protocols vary, particle sizes are classified differently, and environmental pathways are described using different terminologies. Taken together, the evidence base is growing in volume but not always in coherence.
Why this matters now
Non-exhaust emissions from road transportation, which include tire and brake wear, are increasingly in the spotlight as tailpipe emissions decline with the rise of electric vehicles. Regulatory bodies in the EU, UK, USA and beyond are considering how to assess and manage tire wear emissions. The complexity of the current evidence base, however, presents a significant challenge: without a harmonized framework, regulators must navigate data that is often incomplete or inconsistent, making it difficult to establish robust, evidence-based policy.
At the same time, public awareness is rising, leading to mounting pressure for answers. While past research has generated a large volume of data, this science remains siloed. Consequently, without solid, harmonized science, there is a risk of pursuing ineffective solutions. For example, should regulation focus on tire weight limits, vehicle technology, driving speed regulation or road infrastructure? Harmonization is the tool that ensures policy is grounded in the most reliable evidence, not just the loudest opinions.
Lessons from other fields
This is not unprecedented. In other complex fields, harmonization has provided a baseline for scientific progress and coordinated action:
- Good Laboratory Practice (GLP) protocols built trust in chemical and pharmaceutical safety studies.
- WHO air and water quality thresholds created a global baseline for environmental health responses, enabling countries to align efforts.
- REACH chemical safety regulation in the EU succeeded by harmonizing how risk data was reported and assessed.
These examples show how harmonization can accelerate science, inform policy and build public trust.
What harmonization could deliver
Harmonization in tire science could take several forms:
- Shared terminology for TRWP that distinguishes between airborne, dissolved and particulate fractions.
- Agreed analytical guidelines, so that results from different labs can be compared and combined.
- Adapted frameworks for risk assessment, drawing on lessons learned from other fields but tailored to the unique characteristics of TRWP. This includes a tiered methodology that begins with lab-generated materials such as cryogenically milled tire tread (CMTT) and progresses toward real-world roadway samples.
- Validation of the conceptual exposure model, to map how tire wear emissions are generated, dispersed and encountered in the environment.
These steps, outlined in the SOK papers, would enable researchers to close data gaps more systematically, regulators to design proportionate policies and industry to target innovation where it has the greatest impact.
What needs to happen next
The path forward requires coordinated action:
- The industry and the scientific community need to develop and apply harmonized protocols, so new studies add to a coherent evidence base. For example, systematic studies on the effect of electrification of the vehicle fleet on tire wear emissions, and studies on quantification of human and environmental exposure routes.
- Regulators should support the adoption of harmonized frameworks in emerging policy discussions, ensuring rules are based on consistent science. For instance, developing and implementing harmonized sampling protocols for tire wear emissions in the environment.
- Industry should invest in collaborative research and data sharing, helping to test and refine harmonized methods.
Standing at the edge of progress
New analytical methods, modeling techniques and collaborations are emerging, but without coordinated action, the field risks falling short.
The SOK papers offer a path forward by strengthening the scientific foundations needed for the next phase of progress. TIP’s role in supporting this work reflects its commitment to credible science, collective learning and industry-wide solutions, a role it has been playing for several years in partnership with academia.
The opportunity is here – but it will not wait forever. As vehicle technologies evolve, as electrification reshapes transportation and as scrutiny on tire emissions grows, the need for a coherent, harmonized approach will only intensify. The sooner we align, the sooner we can translate scattered insights into credible evidence – and develop meaningful, effective solutions to mitigate tire wear emissions.
About the author
Dr Stephan Wagner is head of the Institute for Analytical Research at the Hochschule Fresenius University of Applied Sciences in Idstein, Germany. He is an expert in the analysis and fate of anthropogenic materials such as tire and road abrasion particles, micro and nano plastics, nanomaterials as well as organic trace contaminants in the (urban) water cycle.
