The team -- Bruce Janson, professor of civil engineering; Wesley Marshall, assistant professor of civil engineering, and Krista Nordback -- found that the average rate of vehicular collisions was definitely lower at intersections that see more than 200 cyclists daily. "Our studies have hypothesized that when drivers expect to see a significant number of bicyclists on the street, their behavior changes," Marshall says. "They are more likely to look over their shoulder for a bicyclist before making a right turn."
Safety Performance Functions, or SPF, are mathematical equations used my multiple departments of transportation to study and predict the number of collisions in a single area based on the factors impacting it. Though the state has SPF in place for cars, there are none for bicycles. Janson, Marshall and Nordback created their own bike-oriented SPF by studying crashes at two intersections in Boulder where more than two-thirds of that city's accidents occur, and weighing the data with the number of bikes in the area.
"Fortunately, Boulder was one of the first cities to establish a bicycle counting program back in the early '90s," Marshall says, and noting that Boulder was ideal for the study given its high rate of cycling, at 12 percent of the population.
Later studies will examine the relation between higher bicycle usage and more conscientious awareness while driving. "In fact, we are beginning to find that cities with a higher level of bicycling are not just safer for cyclists but for all road users," he says. "Improving the streets to better accommodate bicyclists may enhance safety for everyone."