On icy roads, studded winter tires can save lives – but they pulverize pavement and fill the air with dangerous, inhalable particles. A new Swedish study shows that both road wear and airborne particles could be reduced by as much as 20 percent if studs were made instead with an alternative hard metal.

In tests at KTH Royal Institute of Technology in Stockholm, researchers compared asphalt wear-and-tear and particle emissions caused by cobalt-containing studs with studs composed of an alternative, iron-nickel containing hard metal. They found that the iron-nickel stud material could grip ice and packed snow just as well—while causing significantly less damage to the road surface.

“Cobalt is a cheap solution,” says Ulf Olofsson, a professor in the Department of Engineering Design at KTH Royal Institute of Technology. “It’s so hard that it doesn’t wear down, which is why it’s also mass produced for rock drilling tools.”

“But asphalt is soft enough that cobalt-containing studs grind and pulverize it into ultra-fine particles that go deep down into the body when inhaled.”

Studs need to be only 20 to 30 percent harder than asphalt to make driving on ice safer, Olofsson says. “But the studs on the market today are double the hardness of road material and nine times the hardness of glacial ice at -40C.

“That’s overkill,” he says.

Olofsson says the research team is now studying the longevity of alternative stud materials – the next step in finding an alternative to cobalt-containing studs.

Though studies show studded tires save roughly 70 lives each year in Sweden, some cities in the country have banned them on designated roadways due to the health risk posed by airborne asphalt particles. In most U.S. states, use of studded tires is restricted, while several states have banned them altogether. Mostly allowed across Europe, the tires are however banned in several, including Germany, the Netherlands and Poland.

In the EU, non-exhaust vehicle emissions from tire, road and brake wear are equivalent to exhaust emissions in terms of PM10 (particles with aerodynamic diameters smaller than 10 µm), Olofsson says. But in the Nordic countries, non-exhaust PM10 emissions significantly exceed those from exhaust due to the frequent use of studded tires.

It also increases road maintenance costs for the public. He estimates that Swedish road surfaces have a lifespan half as long as the roads in Germany, where a ban on studded tires is in place.