A new U.K. study suggests that passing vehicles are more likely to strike bicyclists who wear helmets than those who ride without the protective gear.

Dr. Ian Walker, a traffic psychologist at the University of Bath, strapped on a helmet and fitted his bicycle with a computer and a distance sensor to record data from over 2,500 overtaking vehicles in Salisbury and Bristol. He was struck two times during the course of the experiment – once by a bus and once by a truck. Both times, he was wearing a helmet.

“By leaving the cyclist less room, drivers reduce the safety margin that cyclists need to deal with obstacles in the road, such as drain covers and potholes, as well as the margin for error in their own judgments," Walker said in a release Tuesday.

“We know helmets are useful in low-speed falls, and [are] definitely good for children, but whether they offer any real protection to somebody struck by a car is very controversial. Either way, this study suggests wearing a helmet might make a collision more likely in the first place," Walker said.

The study found cars on average passed 1.33 metres away from the cyclist, while trucks on average left 1.14 m. Buses on average left the least amount of room at 1.10m.

Walker also put on a wig to see if drivers allotted more space for female cyclists. He found that when wearing the wig, drivers gave him an average of 14 cm more space when passing. The professor said that in future research, he hopes to account for this difference.

Walker's research has been accepted for publication in the journal Accident Analysis & Prevention.