It might be peer pressure. It might be geometry. It’s almost certainly some of each.
But following up on a study that found that (as we reported last year) 94 percent of observed bike users in Oregon stopped for red lights, a Portland State University civil engineering student has also found that every additional person waiting next to you on a bike makes you 78 percent less likely to run the light on your own bike.
That’s assuming that you happen to be riding through one of the seven intersections observed, four of which were at Portland intersections that have dedicated bike signals and are frequented by utilitarian commuters. The intersections in Beaverton, Corvallis and Eugene did not have bike signals.
The new study’s author, Samson Thompson, also measured how much various other factors influence red-light running: gender, the presence of a bike signal, helmet use, the amount of cross traffic, the presence of an adjacent motor vehicle and whether a biker had witnessed a previous violation while approaching the red light.
“The number of cyclists already waiting has the biggest effect by far,” Thompson said Friday, presenting his findings as part of a masters thesis defense. “It’s probably because there are more eyes on the road, but it’s also because bike infrastructure, bike boxes, are not very big. So somebody could be physically impeded from running the red light.”
The second most influential factor in getting people to follow the law while biking: having a car stopped next to them.
Less powerful factors, all of which increased the chance that someone would jump a red lights: witnessing a previous violation, not wearing a helmet, and being male.
In all, the study used video footage and direct observation to capture the decisions of more than 2,500 bike users.
Thompson said he gathered video data from the four Portland intersections because video footage had already been captured there, for a separate of bike-specific signals. He conceded, in his presentation, that it seemed to be a nonrepresentative sample: disproportionately wealthy, white and professional compared to Portland’s bike-using population and its population in general.
“My sense is that people who benefit from the system as a whole are going to be more likely to adhere very staunchly to traffic rules.”
— PSU engineering student Samson Thompson
“My sense is that people who benefit from the system as a whole are going to be more likely to adhere very staunchly to traffic rules,” Thompson said.
In an interview after his presentation, Thompson added that based on his own experience, the decision of a bike user not to weave through a crowd of stopped bikes in order to get past a queue of other riders and jump a red light (even if it’s physically possible) isn’t merely about social pressure.
“It’s not that they’re going to think I’m a jerk,” Thompson said. “It’s more trouble.”
Thompson, an intern at Alta Planning and Design whose study took home first prize last month among student research presentations at TREC’s Oregon Transportation Summit, added that he’s amused by a question he’s never been asked yet.
“It’s funny that nobody asked me if I run red lights,” he said. “I do, on occasion.”