New Formula Determines Which Streets Need Bike Lanes

Daily commute frustrations led to the discovery of the formula, which could be used to help plan cities.

Bike lanes have beenproven to help reduce unsafe passing, and a new study shows which streets are most in need of that safety improvement. (Image courtesy of University of Waterloo.)

Bike lanes have been proven to help reduce unsafe passing, and a new study shows which streets are most in need of that safety improvement. (Image courtesy of University of Waterloo.)

If you’re a cyclist who is sick of dodging cars to stay safe in your daily travels, you may be in luck: researchers have developed a formula to determine which roads have more “unsafe passing incidents”—a formula that urban planners can hopefully use to determine which roads need designated bike lanes.

The study was motivated by one of the authors’ difficulties as an urban cyclist. “I got frustrated by what I perceived as vehicles getting too close to me,” said Bruce Hellinga, a civil and environmental engineering professor at Canada’s Waterloo University. “You feel very vulnerable when a vehicle comes within what feels like mere centimetres.” Hellinga and his fellow authors were interested in “unsafe passing events,” hazardous situations where a driver passes a cyclist too close for comfort. They wanted to come up with a formula for how many such incidents were likely to occur on a given street, so that urban planners could prioritize the more dangerous streets for installing bike lanes.

To get hard data, they examined urban roads around their university. This involved using a specialty bike with an ultrasonic sensor that could measure the distance between the bicycle and the car, and a video camera that helped them interpret bike-car interactions. Using this bike, the researchers took data from 5,227 “passing events.” They decided on a safe passing distance of 1 m (about 3.3 ft), because that’s the legally mandated or suggested standard in some parts of North America.

Perhaps unsurprisingly, they found that having bike lanes in place made unsafe passes far less likely to occur. A two-lane road without a bike lane saw 12 percent of motorists passing with less than a meter between them and the cyclist, while the same road with a bike lane saw just 0.2 percent of motorists doing the same. Four-lane highways are much the same; streets with bike lanes dropped unsafe passing incidents from 6 percent to 0.5 percent.

The researchers also found that one of the biggest determinants of having unsafe passing events was restricted passing: when the car couldn’t change lanes or “move over” to the other side of the lane because there were too many other cars on the street. “Drivers aren’t trying to scare cyclists or be inconsiderate,” Hellinga explained. “In many cases, they just don’t feel they can leave more space because of the geometry of the road and the proximity of other vehicles”.

From their findings, they were able to determine that the factors driving unsafe passing were expected bicycle demand, the length of the road segment, Annual Average Daily Traffic, the speed limit, and the traffic signal timing “upstream” from the segment of the road. The formula is currently being used to develop software that can predict the number of unsafe passes by roads based on these factors. The hope is that this formula can be used to help urban planners figure out which roads need bike lanes the most.

The paper’s authors don’t see their results as encouraging a bike vs. car mentality. “It’s not about giving something to cyclists and taking something away from motorists,” Hellinga said. “It’s about putting in infrastructure to reduce stress levels and improve safety for both.”