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