The US Tire Manufacturers Association (USTMA) will produce cryogenically milled tire tread (CMTT) and provide samples to researchers to advance scientific study on tire and road wear particles (TRWP).

In 2020, independent global emissions testing company Emissions Analytics reported that pollution from tire wear can be 1,000 times worse than what comes out of a car’s exhaust. (Earlier post.) The increased popularity of SUVs, larger and heavier than standard vehicles, exacerbates this problem, as does growing sales of heavy EVs and widespread use of budget tires, the company said.

Non-exhaust emissions (NEE) are particles released into the air from brake wear, tire wear, road surface wear and resuspension of road dust during on-road vehicle usage. No legislation is in place to limit or reduce NEE, but they cause a great deal of concern for air quality. NEEs are currently believed to constitute the majority of primary particulate matter from road transport, according to Emissions Analytics.

The California Air Resources Board (ARB) Vehicle Emissions Research Program is investigating non-exhaust emissions, initiating external research contracts and performing in-house studies to better understand the individual non-exhaust sources. The VERP is also in the process of collaborating with various other agencies and organizations to help understand the scope of this problem.

We know that researchers face limitations in trying to create representative tire and road wear particles for accurate scientific study. To support researchers and advance their work, USTMA is using a standardized methodology to produce cryogenically milled tire tread, samples of which we will provide to researchers who study the potential human health and environmental impacts associated with tire wear particles.

—Sarah Amick, Vice President EHS&S and Senior Counsel, USTMA

CMTT is the product of a standardized and reproducible laboratory process that grinds (or mills) tire tread to simulate tire particles that are normally generated by the friction between tires and road surfaces. CMTT is a mix of tiny rubber pieces that are representative of tire tread but do not contain chemicals or elements arising from pavement or any interactions with pavement.

Overview of tire components and location of tread. Source: “Methods for CMTT Generation”

For researchers who study TRWP, CMTT offers a surrogate material that eliminates external contamination sources that make contact with tires during normal operational use. CMTT is not a direct replacement for the study of TRWP, but it allows researchers to isolate and focus studies on the tire tread component.

Source: USTMA

The methodology used for CMTT production was developed by the World Business Council for Sustainable Development’s (WBCSD) Tire Industry Project (TIP). TIP’s aim is to contribute to a more sustainable future by proactively identifying and addressing the potential human health and environmental impacts associated with the life cycle of tires.

The Tire Industry Project created this methodology to support research on tire wear by providing a reliable and affordable material for lab experiments. With more than a decade of experience researching TRWP and producing tire test materials we understand the scientific importance of representative test materials; CMTT is complicated and costly to produce, and we support efforts to remove barriers to the use of appropriate materials for TRWP research.

—Anne Cécile Rémont, Director of TIP

Researchers who are interested in learning more about CMTT and obtaining a CMTT sample for research may submit a request via the USTMA website. USTMA hopes to have CMTT samples available to ship to researchers as early as the second quarter of 2022.

Resources

• Beate Baensch-Baltruschat, Birgit Kocher, Friederike Stock, Georg Reifferscheid (2020) “Tyre and road wear particles (TRWP) - A review of generation, properties, emissions, human health risk, ecotoxicity, and fate in the environment,” Science of The Total Environment, Volume 733, doi: 10.1016/j.scitotenv.2020.137823 (open access)