An annual report by the Governor's Highway Safety Association finds that motorcyclist traffic fatalities rose 10% across the nation between 2014 and 2015, and the increase was substantially greater in Michigan.
Fatal motorcycle accidents rose 23% in Michigan.
Co-author Richard Retting says there could be many factors responsible, including better weather in 2015, along with more vehicles of all kinds on the highways.
But he says Michigan's repeal of its mandatory motorcycle helmet law in 2012 very likely was a factor, too.
"It's almost a certainty," says Retting. "The effectiveness of a helmet is so well established. The lack of motorcycle helmet laws, which is becoming unfortunately ubiquitous across the country, contributes to the number of fatalities."
The report also notes that more motorcycle accidents in Michigan involved alcohol and drug use than other kinds of vehicle accidents.
Retting says there are many things that reduce the riskiness of motorcycle riding - including wearing a helmet, not speeding, wearing bright, reflective clothing, and not using alcohol or drugs while riding.
But motorcycles will always remain the least safe form of highway transportation, he says, with a fatality rate 26 times that of cars and trucks.