In response to our friends question about bike culture in Ann Arbor--specifically the high incidence of helmet-less sidewalk riding--I have come to a different conclusion than Mr. Houston: people bike like this because people are terrible at judging risk. Just look at parents top 5 fears for their children versus the top 5 ways children get hurt or killed. Thinking abstractly, biking on the sidewalk seems much safer than biking in the road: being hit by a 1300 kg Carolla causes a lot more damage than being hit by a 75 kg pedestrian. Unfortunately, a cursory analysis like this though, vastly over simplifies this system. Very little research has been done on bicycle transportation planning. Thus, the majority of bicycle infrastructure, policy, and strategy is based on what amounts to rumor and folklore.
While riding on the sidewalk may feel safer, the few studies that have been conducted show that biking on the sidewalk carries between 1.8 and 4 times the risk of accident than biking in the street. In fact, the only thing that carries more risk than biking on the sidewalk is biking against traffic. Why is this? Sidewalks confine bicycle travel and hinder the ability of drivers to see cyclists. Drivers checking for pedestrians before entering an intersection are not conditioned to look for cyclists traveling at speed. Most bikers greatest fear, in terms of bike-car collisions, is being overtaken from behind by a car traveling in the same direction. This type of accident though, is the least frequent category of car-bike accidents; it is far more likely to be hit in an intersection. The final reason cyclists should not ride on sidewalks is that they end up having to weave around pedestrians who are milling around in near Brownian motion. Riding in the sidewalk increases the risk of both being hit by a car and hitting a pedestrian. It is far better to develop the skills and confidence necessary to bike on the streets. Also, helmets are hot:
Is cycling dangerous? The risk of bicycle use: accidents, fatalities, injuries, and benefits
Risk Factors for Bicycle-Motor Vehicle Collisions at Intersections
Adult Bicyclists in the U.S.
The Dilemmas of Bicycle Planning
Photo: Flyboy Helmet via Nutcase Helmets