A state survey has found that 73 percent of Michigan motorcyclists wear helmets, down from seven years ago when almost all riders used them.
Michigan ended mandatory universal helmet use in 2012, letting riders opt out under certain circumstances.
The Michigan Department of Highway Safety said Monday that helmet use varies widely among types of riders, with chopper and custom bike riders less likely to wear helmets and sport bikers more likely. Female riders and those under 30 and over 60 also wear helmets more frequently.
Wayne State University's Transportation Research Group observed motorcyclists this summer.
The report says Michigan helmet use is down from 99.4 percent in 2006, the last year there was a comprehensive survey.