DETROIT — U.S. Motorcycle deaths spiked 10 percent last year, topping 5,000 for the first time since 2008, according to a study done for a highway safety group.

The annual study for the Governors Highway Safety Association attributes the increase mainly to increased travel nationwide and better weather leading to a longer riding season in many states. Low fuel prices also contributed to a 3.5 percent rise in motor vehicle miles traveled last year over 2014, according to federal data.

Study researchers from Sam Schwartz Consulting say a big change that could cut motorcycle deaths would be restoring mandatory helmet laws in 32 states that don’t have them for all riders.

The study used preliminary state data to count 5,010 motorcycle deaths last year, up 450 from 2014. The increase is consistent with preliminary numbers from the government that show traffic deaths overall rising an estimated 8 percent last year after trending downward for a decade.

The association suggests that motorcyclists cut risks by wearing government-approved helmets and bright clothing to be more visible, obeying speed limits and never riding while impaired by alcohol or drugs.

The number of deaths last year is about double the annual number through the 1990s.