You may never forget how to ride a bicycle, but should you forget your helmet when you hop on your two-wheeler?

About a year ago a psychologist at the University of Bath in England announced the results of a study in which he played both researcher and guinea pig. An avid cyclist, Ian Walker had heard several complaints from fellow riders that wearing a helmet seemed to result in bike riders receiving far less room to maneuver—effectively increasing the chances of an accident. So Walker attached ultrasonic sensors to his bike and rode around Bath, allowing 2,300 vehicles to overtake him while he was either helmeted or bareheaded. In the process, he was actually contacted by a truck and a bus, both while helmeted—though, miraculously, he did not fall off his bicycle either time.

Cancels Out Its Protection

Walker's findings, published in the March issue of Accident Analysis & Prevention, state that when he wore a helmet drivers typically drove an average of 3.35 inches closer to his bike than when his head was not covered. But if he wore a wig of long, brown locks in lieu of a helmet—appearing to be a woman from behind—he was granted 2.2 inches more room to ride.

“The implication,” Walker says, “is that any protection helmets give is canceled out by other mechanisms, such as riders possibly taking more risks and/or changes in how other road users behave toward cyclists.” He cannot explain the extra leeway granted to him when he pretended to be a woman, although he speculates that drivers might perceive members of the fairer sex as less capable riders, frailer or just less frequent bikers than men.

Still Enough Room to Ride, Right?

Randy Swart, founder of the Bicycle Helmet Safety Institute, asserts that studies such as Walker's run the risk of misleading cyclists as to the effectiveness of helmets. “The cars were giving him, on average, a very wide passing clearance already,” he explains, noting that most vehicles typically stayed well over three feet from Walker's bike, rendering the 3.35-inch discrepancy insignificant.

Walker reanalyzed his data recently to address this line of reasoning. “I assessed the number of vehicles coming within one meter [roughly 3.3 feet] of the rider, on the principle that these are the ones that pose a risk,” he says. “There were 23 percent more vehicles within this one-meter danger zone when a helmet was worn, suggesting a real risk.”

Before Walker's paper came out, Dorothy Robinson of the University of New England in Armidale, Australia, published a review article in the British Medical Journal about what happened after regions in Australia, New Zealand and Canada introduced legislation that spurred a more than 40 percent increase in bicycle helmet use among their populaces. The rates of bike accidents involving head injuries were on the decline before the newly instituted laws, and she found the new mandates did not result in a sudden drop-off in the percentage of cyclists sustaining head injuries.

Should You Protect Your Noggin?

Coincidentally, around te same time that Walker announced his results, New York City released a report on bicycle deaths and injuries strongly suggesting that helmets do reduce head injuries: 225 cyclists died between 1996 and 2005 on city streets; 97 percent of them were not wearing helmets. Of these deaths, 58 percent are known to have involved head injury, but the actual number could be as high as 80 percent. Comparing the helmet to a seat belt in a car, Swart says, “When you do have that crash, you had better have it on.”

In agreement with Swart are officials at the Centers for Disease Control and Prevention, who point out that helmets are considered an effective way to help prevent head injuries from bicycle mishaps. Walker will not make specific recommendations to other cyclists about whether to wear headgear. But he does urge people to read the research. And watch out for cars.