Bicyclist deaths have been on the rise nationwide in the past few years, and one of the biggest jumps was seen in California — where 338 people died while biking between 2010 and 2012, according to a new study that also looked at some common factors in the deaths.

The deaths, the Governors Highway Safety Association reported, are in part due to an expanding commuter culture. The number of bicycle commuters in the U.S. has jumped 62 percent since 2000, according to 2013 Census Bureau data.

The new report assessed data from 2010 to 2012. California was one of six states that, together, made up 54 percent of bike fatalities across the country. California’s death toll climbed from 100 in 2010 to 123 in 2012 — outpacing a 16 percent national increase in the same time frame. Meanwhile, motor vehicle fatalities increased by 1 percent nationally.

Some common factors in cycling deaths may not be surprising. Two-thirds of those killed in 2012 were not wearing helmets, and more than a quarter of riders over the age of 16 who died had blood-alcohol levels of .08 or higher (the legal limit for driving in California).

But other findings were a bit more eye-opening. Over the years, the age of riders in deadly crashes has gone way up — people 20 or older made up 21 percent of victims in 1975, and 84 percent of victims in 2012 — and they are more likely to be men.

“The percentage involving males increased from 82 percent to 88 percent” from 2010 to 2012, the report states. “Adult males comprised 74 percent of all bicyclist deaths in 2012.”

Bicycle fatalities are increasingly centered in urban areas, which saw half of all deaths in 1975 and 69 percent in 2012.

That’s not a surprise to in San Francisco, where ridership nearly doubled between 2006 and 2013, according to the San Francisco Bicycle Coalition. Four cyclists were killed on the city’s streets in 2013.

Jonathan Adkins, executive director of the Governors Highway Safety Association, said reducing fatalities in cities like San Francisco is a priority. He lauded efforts to keep cyclists and cars separate, such as Muni’s plan to build a separated bike path on the city’s busy Embarcadero.

“There’s more biking in general, and more biking in urban areas,” Adkins said. “But you’ve got to protect cyclists when they’re out there on the road with motor vehicles. This is a share-the-road situation.”