(HealthDay News) -- The number of bicyclist fatalities in the United States is increasing, particularly among adults in major cities, a recent study shows.
After decreasing from 1975 to 2010, the number of bicyclists killed annually increased by 16 percent from 2010 to 2012. More than 700 bicyclists died on U.S. roads in 2012, according to the Governors Highway Safety Association.
The study also reported that the percentage of these deaths that occur in densely populated urban areas has risen from 50 percent in 1975 to 69 percent in 2012.
"We've seen a gradual trend over time where more adults are bicycling in cities, so we need cities to develop ways for cyclists and motorists to share the road," said report author Allan Williams, former chief scientist at the Insurance Institute for Highway Safety.
But, the report also pointed out that many of the deaths were potentially preventable. Two-thirds of the deaths occurred in people who weren't wearing a helmet, the researchers found. And, in 2012, almost 30 percent of the deaths were in people who had a blood alcohol content level above the legal driving limit of 0.08 percent, according to the study.
One of the biggest shifts in cycling deaths was the average age of the victims. Eighty-four percent of bicycle deaths were in adults in 2012. That compares to just 21 percent in 1975, according to the study. Overall, adult males accounted for 74 percent of the bicyclists killed in 2012, the researchers reported.
The new research also found that states with high populations and multiple cities accounted for the majority of bicycle fatalities. Between 2010 and 2012, California, Florida, New York and Texas had nearly half of the country's total bicyclist fatalities.
Part of the explanation for the increasing number of bicycle deaths is that more people are bicycling to and from work, the report suggested. Nearly 300,000 more people biked to work in 2008 to 2012 than in 2000, according to U.S. Census data.
"There has been a national movement to get people out walking and biking because it has major benefits for their health, and for the environment," said Jacob Nelson, director of traffic safety advocacy and research with the Automobile Association of America.
"While it is important to encourage more people to walk and bike, we need to think about how we manage a growing number of vulnerable road users," Nelson said. "Policy makers who are vocal advocates for walking and biking need to also be vocal advocates for creating safe environments for bicyclists -- and I'm not sure that always happens."
Some cities have developed more bike lanes and changed traffic patterns to accommodate the increasing number of bicyclists on their roads, according to the report. These methods may create a barrier between motor vehicles and cyclists, making the roads a safer place for cyclists.
Another important step in reducing bicycle fatalities is the consistent use of a helmet. Wearing a properly fitted helmet significantly reduces the chances of having a serious head injury, according to Williams. But, nearly half of American adults never wear a helmet while riding a bicycle, according to background information from the report.
"It's unfortunate that there is no adult law requiring helmets," said Williams, who noted in the report that 21 states have helmet laws for minors. "The best we can do is to take an educational approach by telling people that helmets can protect people from traumatic head injuries, and that many fatal accidents involve injuries to the head," Williams said.
About one-fourth of crashes happen in darkness, so wearing reflective clothing or attaching a light to the bicycle can help motorists notice cyclists, Williams advised. And, as with driving a motor vehicle, don't drink alcohol before cycling, the researchers cautioned.
"Bicyclists must remember that they have to follow the same rules as motor vehicles," Williams said.
The report was published recently by the Governors Highway Safety Association.
Find out more about safe biking at the U.S. National Highway Traffic Safety Administration.