A team of Earth scientists poses a question to the environmentally conscious among us: How hard do you ride your brakes? At this point, a lot of people have embraced the idea that it’s probably not a bad idea to use a metal straw instead of a plastic one to help combat microplastics in the environment, but what about the particles left behind when we drive our cars?

When we think of microplastics, we may envision an ocean littered with straws, or even human guts riddled with plastic pellets. But as scientists continue to research microplastics, it’s becoming clear that the problem goes beyond the ocean, stretching all the way inland to major highways, where cars shed tiny pieces of rubber and brake pads as they speed by. A recent analysis of the air quality surrounding German highways unveiled this month at the Geological Society of America’s annual conference in Indianapolis builds upon earlier findings. As lead study author Reto Gieré, Ph.D., chair of the University of Pennsylvania’s Earth and Environmental Science Department tells Inverse, when you take a closer look, these particles are more harmful than we initially thought:

“The Important thing is that these particles won’t go away even if we have electric cars,” he says. “Electric cars will change the emissions, but they won’t change the abrasion particles from the tires or the road surface or from the brakes.”

microplastics traffic
Rethinking how we design roads and traffic flow might help fix the issue of microplastics cause by abrasion 

It’s already estimated that roughly one kilogram — 2.2 pounds — of rubber is shed from a single tire over the course of its lifetime, which can happen as a result of the abrasion that comes from a tire simply rolling along the road surface, as well as the constant wear of slamming on the brakes. Gieré’s work shows just how much this material hangs around: He found that roughly 89 percent of particles lingering in air near several major German highways were due to this process.

Specifically, this study looked to investigate what these tiny rubber bits look like on a microscopic level. To do this, Gieré and his team used automated transmitted-light microscopy (TLM), a technique that allowed them to analyze the components and mass of each individual particle. Here, they found that these microplastics are made of a rubber “core” but that they often form an “entrustment” when they linger on the road surface.

“These tire particles end up on the road, with cars driving over them again and again and again. So they’re rolled around and suspended and deposited again where a new car can drive over it,” Gieré explains. “So this creates a lot of possibility for tire particles to pick up other dust particles that are lying on the road, so this ends up as a crust on the tire particles,” he adds.

While these particles may be rubber at heart, they also can sport loads of other components. For example, Gieré highlights certain metals like iron, copper, and antimony (a metalloid, not strictly a metal), which can be toxic if inhaled. But he adds that its hard to be sure about what else might lie inside a tire particle crust unless manufacturers provide a full list of what’s inside their tires.

Since our driving habits may be creating an unexpectedly large environmental burden, Gieré suggests that we rethink how we design traffic flow — he hopes that if we reduce braking we may be able to at least halt some of the abrasion that releases these crusty particles into the air:

“What we think is that if you slow down the traffic, so instead of having congestion where every few meters you have to stop again because traffic is so congested you should have a mandatory speed of five miles per hour or so, but no stopping.”

To be clear, he’s not arguing that you run any red lights for the sake of the environment, but in general, redesigning highways or road systems to minimize the time spent in bumper-to-bumper might be a win-win, both for our sanity and for the environment.