The number of people who died in motorcycle crashes last year jumped 10 percent, a sobering reminder as the warmer weather draws more motorcyclists onto the roads, according to a new report.

Safety advocates say the increase comes in part because 31 states no longer require motorcyclists to wear helmets. Riders who discount the need for helmets say that is not the cause.

The Governors Highway Safety Association projects that motorcycle fatalities for 2015 will be 5,010, only the third time they have exceeded 5,000, and the first time they did so since 2008. They increased in 31 states, including Maine, dropped in 16 states, and remained flat in three states and the District of Columbia, where there were three.

The association projects motorcycle deaths in Maryland will increase by five to a total of 74 deaths in 2015, and drop by 11 in Virginia, with 79 deaths in 2015.

Although motorcycles are a small fraction of the number of vehicles on the road, they account for nearly 15 percent of roadway fatalities.

Under federal pressure in 1967, all but three states mandated that motorcyclists wear helmets. But after Congress ended federal authority to enforce penalties, laws requiring all riders to wear them have been repealed in 31 states, although some still require them for young or novice riders.

“The most important injury protection mechanism for motorcyclists is to wear a DOT-compliant helmet, ” the GHSA report says. “Helmets reduce head and brain injuries and decrease the risk of dying in a crash by 37 percent.”

Richard Retting, one of the report’s author’s said his work provides “a stark reminder of how susceptible motorcyclists are to fatal and life-threatening injuries.”

“The risk of motorcycle crashes and fatalities is compounded by factors such as alcohol and drug use, increased speed limits, the repeal of state helmet laws, and a record number of vehicles on U.S. roads,” Retting said.

Though 2015 data wasn’t available to reflect how many riders who died were legally drunk, a year earlier 29 percent of those killed had a blood-alcohol level above the legal limit of .08. By contrast, 22 percent of drivers killed in other vehicles were above the limit.

The GHSA’s preliminary statistics provide the first look at last year’s motorcycle deaths. The GHSA’s members are the heads of each state highway safety office, and the data they collect is forwarded to Washington to be compiled into annual statistics by the National Highway Traffic Safety Administration.