A Melbourne street at rush hour during WW2

Safety in Numbers

Confirming an oft-quoted concept, that there is safety for cyclists in numbers, is a recent US study by researchers from the University of Colarado Denver.

The ‘safety in numbers’ effect is often cited as one of the reasons for the increased safety of riders in countries like the Netherlands, compared to countries such as Australia and the United States, where many motorists rarely see a rider.

Researchers from the University of Colorado Denver set out to model the mathematical relationship between the frequency of crashes and major factors related to them for bicycles in the city of Boulder, Colorado. Boulder was chosen because it has one of the highest rates of commuter cycling in the United States, according to study co-author Wesley Marshall, who is assistant professor of civil engineering at the College of Engineering and Applied Science.

With 12 percent of the population cycling it is one of the few US cities with enough people cycling to achieve the safety benefits already documented by researchers in Europe, said Dr Marshall. The other factor that made Boulder ideal is that it was one of the first cities to establish a bicycle counting program back in the late 90s. Researchers studied crashes at intersections throughout the city where more than two-thirds of collisions occurred and compared the crash data to bicycle count data.

Intersections with less than 200 cyclists per day had a higher risk of accidents. “Anywhere above this threshold is where we are seeing the largest safety benefits,” Dr Marshall said.

While the research confirmed what many cyclists intuitively feel it did not establish the reasons why.

“Other studies have hypothesised that when drivers expect to see a significant number of bicyclists on the street, their behaviour changes,” he said. “They are more likely to look over their shoulder for a bicyclist before taking a right turn.” The author’s next study plans to explore possible reasons.

Reasearch like this has implications for all road users not just those choosing to ride. “In fact, we are beginning to find that cities with a high level of  cycling are not just safer for cyclists but for all road users,” Dr Marshall said.  “Improving the streets to better accommodate bicycles may enhance safety for everyone.”

The study was co-authored by Bruce Janson, professor of civil engineering, and Krista Nordback. It was published in the journal Accident Analysis & Prevention and is available on request.