Last week Grist had a great article about “safety in numbers” for cyclists. Research within the US and around the world has shown that as bicycling rates go up, the total number of crashes stays flat, resulting in a significant decrease in bicycle crashes per trip. While this might initially sound counterintuitive, the premise is pretty simple. The more cyclists a city has, the more drivers expect cyclists, and drive accordingly. Similarly, as bicycling rates increase, drivers are more likely to be cyclists themselves, causing further behavioral changes that improve the safety of bicycles.

The phenomenon, dubbed “safety in numbers,” was first identified in 2003, in an academic paper by public health researcher Peter Jacobsen [PDF]. After being asked by officials in Pasadena, Calif., if their city “was a dangerous place to bicycle,” Jacobsen began looking at crash data from various communities where bicycle ridership had fluctuated over time. What he found surprised him: The number of crashes involving bikes correlated with the number of riders in a community. As ridership fluctuated, so did the crash rate. More riders, fewer crashes; fewer riders, more crashes. This happened too abruptly, Jacobsen decided, to be caused by slow-moving factors like infrastructure development and cultural change. Bicycling becomes safer when the number of riders increases, he concluded, at least in part because the number of riders increases. The inverse happens, as well. One data set Jacobsen looked at covered 49 years of biking history in the United Kingdom. Those numbers showed that cycling became safer during the oil crisis of the 1970s, caused by the OPEC oil embargo. Once the crisis ended, both ridership and safety dropped.

More after the jump.

For me this brings up two points about bicyclist safety from a public health perspective that almost always get glossed over. First, helmets are a distraction when it comes to the overall safety of bicycling in a city. Helmets are solely about harm reduction. They do not prevent collisions from occurring, they simply reduce the severity of injury caused by blunt force impact to the head. Put another way, even if 100% of cyclist wore helmets it would do nothing to reduce the incidence of crashes.

Second, the primary purpose of bike facilities, in my view, is about getting people that are “interested but concerned” out biking. This segment of the population has the largest immediate growth potential and are what makes the difference between the left and right in the graphic above. Bike facilities entice these types of people to bicycle, creating a virtuous cycle of improved safety, real and perceived, because of “safety in numbers”. This leads to more people biking, and so on and so forth.

This is what you find in every Western country with high bicyclist safety. Lots and lots of people riding, without a helmet in sight, on high quality segregated bike facilities.