In research that may surprise off-road riding enthusiasts and safety experts, a Johns Hopkins team has found that crashes involving ATVs -- four-wheeled all-terrain vehicles -- are significantly more dangerous than crashes involving two-wheeled off-road motorcycles, such as those used in extreme sports like Motocross.

The research, to be presented at the American College of Surgeons' 2010 Clinical Congress in Washington, D.C., this week, found that victims of ATV crashes were 50 percent more likely to die of their injuries than similarly injured victims of off-road motorcycle crashes. ATV victims were also 55 percent more likely than injured motorcyclists to be admitted to a hospital's intensive-care unit and 42 percent more likely to be placed on a ventilator.

"There's a belief that four wheels must be safer than two," says Cassandra Villegas, M.P.H., a research fellow at the Johns Hopkins Center for Surgery Trials and Outcomes. "But we found the opposite. People involved in ATV crashes are more likely to die or suffer serious trauma."

The growing popularity of off-road vehicles in the United States has led to a steep rise in the number of injuries resulting from their use. In 2000, Villegas notes, there were 92,200 injuries involving ATVs or off-road motorcycles; in 2007, the last year for which data is available, there were 150,900 injuries. But little rigorous research has been done to determine which vehicles may be riskier than others.

ATVs and off-road motorcycles are designed for recreational use, not use on city streets, and typically are ridden on trails, sand dunes and other rough terrain.

In the first study to compare the severity of injuries sustained by ATV versus off-road motorcycle riders, Villegas and senior author Adil H. Haider, M.D., M.P.H., an assistant professor of surgery at Johns Hopkins, reviewed data on nearly 60,000 patients who suffered an injury after a crash involving one of the vehicles between 2002 and 2006.

The researchers say they don't know why ATV crashes lead to greater injury and mortality, noting they cannot trace the differences solely to helmet use even though 60 percent of motorcyclists were wearing helmets as compared to 30 percent of those in ATV crashes. Even when both types of riders had been wearing helmets, ATV riders still experienced worse injuries and outcomes than motorcyclists, Villegas says. Only a few states have laws requiring the use of a helmet when riding an ATV, says Villegas, and while motorcycle helmet laws are also determined by states, many more have helmet-use laws for motorcycles.

The researchers say it's possible that ATV riders wear less protective clothing than off-road motorcyclists when they head out, sometimes little more than shorts and a T-shirt. Another contributing factor could be the significant weight of ATVs, which can cause severe crush injuries when they land atop victims and lead to a greater likelihood of internal organ or extremity damage, Villegas says.

Villegas says that these findings may allow parents, legislators, educators and those in the ATV industry to make better decisions about the use of the off-road vehicles. She also says that studies like these could help ATV manufacturers design and implement increased safety technology in ATVs, similar to how automobile manufacturers have used research to make safer cars and trucks.

Hopkins researchers Stephen M. Bowman, Ph.D.; Eric B. Schneider, Ph.D.; Elliott R. Haut, M.D.; Kent A. Stevens, M.D., M.P.H.; and David T. Efron, M.D., contributed to this study.