Editor’s note: Thanks to contributor Mathews Hollinshead, Streets.mn became aware of the growing problem of tire pollution and its impacts on our environmental system. Part 1 of this two-part series examines the impacts of tire pollution generated by in-use tires. In part 2, we’ll look at pollution generated by out-of-use tires and tire recycling programs.
As every resident of and visitor to the United States knows, traveling around this country without a car, within or between cities, is challenging. The U.S. is built in a uniquely car-dependent fashion; as such, according to the U.S. Department of Transportation Federal Highway Administration, there are roughly 283 million vehicles on our roads.
We center the discussion of pollution from these cars on their tailpipe emissions, studying atmospheric carbon deposits from internal combustion engines and their contribution to climate change. These effects are enormous and important to understand (vehicles traveling along roads — including cars, light and heavy trucks, and buses — emitted 1.3 billion metric tons of carbon dioxide equivalent, according to the U.S. Environmental Protection Agency (EPA) Emissions Inventory for 2022); however, they only tell a part of the story.
Underneath every car on the road sits another source of pollution: tires.
Why Worry About Tires?
Though often overlooked, tires are a major contributor to vehicular pollution. A study from Imperial College London estimated that, in 2021, more than 50% of vehicle particulate emissions originated from tires and brakes rather than the tailpipe. As a car travels, its tires break down by way of contact with the road, causing them to shred and leave composite fragments on the road. The EPA study “Where the Rubber Meets the Road: Emerging Environmental Impacts of Tire Wear Particles and Their Chemical Cocktails,” explains how, after the tire deposits particles onto the road surface, wind and rain carry them from the road, permeating our environment and our bodies. According to a study conducted by the San Francisco Estuary Institute, the 5 Gyres Institute, the University of California-Davis and the University of Toronto, “untreated stormwater runoff samples collected [in the San Francisco Bay region] … contained 15.9 tire particles per liter, almost 50% of all microparticles in the samples.”
Tire pollutants pervade our environment with the same intensity as tailpipe emissions, yet none of the 50 states has any regulations protecting public health from tire particulate matter. This failure to recognize the environmental impact of tire pollution is likely due to the erroneous assumption that tire pollution is constrained to large chunks of rubber breaking off and being captured in drains to ultimately cause no environmental or health problems; however, particulate matter ranges in scale from 10 nanometers (small enough to be inhaled and enter our bloodstream) to 1,000 micrometers (large enough to be seen by the naked eye). Once in the body, these particles permeate the blood and, via the circulatory system, the entire body.
The chemical makeup of tires also raises concern. “Where the Rubber Meets the Road” found “heavy metals, natural and synthetic rubber, plastics, hydrocarbons, and traces of other chemicals (e.g. 6PPD),” all of which can have detrimental health effects and, when combined, “emit carcinogens and radioactive compounds.” Highway runoff containing tire pollution has been linked to salmon mortality in urban and suburban streams in California, according to a study organized by the EPA and National Science Foundation. Although the full extent and concentration of tire wear particulate matter’s permeation of the environment is unknown, the independent testing and data specialist firm Emissions Analytics conducted testing which determined that tires produce roughly 2,000 times the particulate matter of tailpipes, with a wider variety of particle sizes and compounds. This level of pollution vastly exceeds the legal requirements for tailpipe emissions. Still, tire emissions remain unregulated.
Tire pollution does not solely originate on the road, either. Once tires have been retired, they are relegated to tire dumps or junkyards, where they continue to break down and pollute the environment. (More on that in part 2 of this Streets.mn series.)
Interestingly, among the best places to avoid tire pollution is the inside of a car. Most modern vehicles have high-quality air filters that scrub the incoming air for particulate matter generated by other cars on the road; however, these filters are absent in almost every other setting in daily life.
The Norwegian Institute for Water Research measured the level of tire pollution near roads in snowbanks, finding that “the concentrations of tire particles in roadside snow [was] within the range where toxic effects on some organisms have been confirmed by previous studies.” The presence of tire pollution in snow banks indicates there is particulate matter in the air surrounding our roads and that it settles into the surrounding environment. The Conference of European Directors of Roads conducted a similar investigation focused on particulate pollution imbuing waterways via road runoff. Across the European continent and surrounding waters, the Conference found tire wear particles occurring “in relatively high concentrations compared to microplastics in general.”
These studies establish an alarming pattern of composite particulate matter and microplastics saturating the soil and water in rural areas, allowing them to contaminate fields, forests and farmlands bordered by highways, ultimately finding their way into our food and the food of other animals. In urban areas, particulate matter and microplastics hang in the air near every street, storefront and park. Just as roads facilitate our transportation, so do they facilitate the transportation of the pollutants they produce.
So, What Do We Do About It?
The assumed solution to vehicle-related pollution is the introduction of electric vehicles; however, they are not the answer for this particular issue. Tire pollution production is directly related to vehicle weight: The heavier the vehicle, the faster the tires wear down. Automotive batteries weigh more than internal combustion engines (ICE), making the average fully electric car roughly 20% heavier than its traditional ICE counterpart; thus, their tires degrade more quickly. Policymakers and car manufacturers must be proactive by addressing tire wear in both the short and long term.
In the short term, improved regulation of tire composition will focus public attention on the issue and force companies to rethink tire design and limit particle emissions, just as it did with tailpipe emissions. The Minnesota Pollution Control Agency (MPCA) has various emission control programs that focus on air and water quality; yet, when it comes to vehicles, the regulations discuss solely tailpipe emissions. The MPCA considers heavy metals, fine particles (dust, dirt and composite particles 10 nanometers to 1,000 micrometers in size) and aromatic hydrocarbons as regulated air and water pollutants from tailpipe emissions. These emission products constitute the majority of pollutants originating from tires; thus, expanding regulation and grant offerings to curtail the impact of tire particulate matter is a straightforward solution.
Ultimately, although it is not feasible to eliminate tires from our society, we can substantially limit their number through the reintroduction of public transit as a practical and accessible form of transportation. The Environmental Research Group at King’s College London measured tire pollution at various locations in three cities — London, Los Angeles and Tokyo — and found increased pollution in areas with higher road speeds and traffic densities.
While not as populous as the studied cities, the Twin Cities has similar road infrastructure that allows pollution to flourish. Metro Transit’s efforts to reduce car traffic between Minneapolis and St. Paul — the Green Line extension, Blue Line extension and Gold Line project— seek to improve the mobility of people without a personal vehicle. But to sufficiently reduce particulate matter emissions, the scope of these projects must expand to replace inter- and intra-city travel on large highways. Routes such as Interstate 94, I-35, I-394, MN-36, MN-280 and MN-55 create the ideal conditions for generating tire pollution, as tire particulate matter emission is directly related to vehicle speed and vehicle weight.
The Minnesota Department of Transportation’s (MnDOT) Rethinking I-94 project provides an elegant solution to this problem. Rethinking I-94 presents various futures for the interstate; but, the most promising and beneficial is the proposal of a mixed-use-zoned parkway featuring rapid public transit to replace the stretch of I-94 between Minneapolis and St. Paul. Reconceiving the interstate would reduce the amount of road space available for generating pollutants, reduce the speed at which personal vehicles can travel and maintain the average travel time between the two downtowns.
In addition to reducing particulate pollution into the air, water, ground and our bodies, creating a vibrant community center would be economically beneficial to the neighborhoods through which I-94 runs, providing new, densely built housing and commercial opportunity. MnDOT does not restrict these improvements to the Twin Cities metro area; transformative projects like the Borealis Train (a partnership with the Wisconsin and Illinois departments of transportation, with federal funding) provide residents across Minnesota access to affordable regional transit that produces no tire pollution, as does Metro Transit’s Northstar Commuter Rail.
As communities and neighborhoods across Minnesota become more walkable and bikeable, as local and regional transit expand, and as commercial and residential areas synthesize, the need to travel long distances for daily activities decreases. The natural consequences are a reduction in usage of personal vehicles and progression toward a healthier, less polluted future.
Environmental issues on the scale of tire pollution can feel overwhelming to the individual; the scale of the problem is so vast and the mechanism of the problem so heavily ingrained in our society that individual action feels inconsequential. Tire pollution cannot be addressed in an isolated, direct manner — it cannot be solved solely through treatment of the symptoms. So, let’s address the underlying causes. As we better understand the impacts of the industrialized world on the environment and human health, we must remedy the underlying causes of the negative externalities. Building new housing, new railroads and bus lines, and renovating highway systems will not innately eliminate tire pollution — these actions will not inherently remove tires from roads.
However, these actions will create the conditions under which fewer people will need cars to live their lives. Alleviating tire pollution, like any entrenched systemic issue, requires a restructuring of our economic and infrastructural systems. But, rather than evaluating potential solutions in terms of cost, we must consider what we can gain by addressing them. Each environmental issue we face affords us the opportunity to unite across our differences and improve the well-being of every member of our society.