Dangerous Left Turn Crashes Can Be Reduced, New Study Finds

Left turns at intersections are a serious problem in many parts of the country.  In 2019, 40% of traffic deaths in San Francisco were caused when drivers made left turns and didn’t see anyone in the crosswalk until it was too late.

To combat the deadly trend, the San Francisco Municipal Transportation Agency (SFMTA) tested traffic interventions aimed to reduce unsafe left turns at seven high-crash test intersections. It found a 17% reduction in average speed and a 71% reduction in the likelihood of a car turning left at higher speeds over 15 mph.

“With diligent research, innovative engineering, creative and personable messaging, behavioral science components and a community-first educational campaign,” Jeffrey Tumlin, SFMTA director of transportation, said in a statement, “we are elated to implement these proven treatments to maximize safety on city streets, end deaths and reduce severe injuries because everyone deserves to feel safe in San Francisco.”

The agency’s report, “A Turn Toward Safety: The Safer Intersections Project,” was released earlier this month to encourage the adoption of safer left turn behavior.

The report’s findings were based on the agency’s analysis resulting from the “Left Turn Traffic Calming Project,” which incorporated a series of measures to encourage slower, wider left turns and increase drivers’ awareness of other road users. These included the installation of waist-high vertical delineator posts and small rubber speed bumps, and the use of paint to create enhanced center lane lines and safety zones.

Researchers collected left-turning driver speeds before and after installation and then compared those at the seven project intersections with four other control intersections. Results indicated that the measures slowed driver speeds and encouraged safer left turns for both people in the crosswalks and opposing traffic, the study noted.

The Insurance Institute for Highway Safety, a nonprofit financed by the insurance industry, addressed the issue in a study last year. Simple, low-cost changes make intersections safer for walkers, its report showed.

In addition to street engineering calming treatments to slower speeds, the project included an education and community outreach campaign, “Safety—It’s Your Turn,” which presented three safer left turn behaviors: Take it slow—5 mph is safest; Make it square—90-degree angles are best; and Stay aware—look out for cars, cyclists, and people. The agency’s report said the campaign was effective in helping to reduce speed.

The SFMTA also collaborated with the Behavioral Insights Team, a behavioral science organization, to analyze how drivers make left turns in order to develop interventions that would prompt safer driving behavior.  

The combination of changing the physical architecture of intersections and the impact of the educational campaign worked by encouraging people to make safer left turns and increasing awareness of how individual actions impact the community, according to the study.

“Pedestrian and cyclist deaths are a growing public health crisis, and streets built to maximize speed continue to put us at risk,” Michael Hallsworth, managing director of BIT Americas, said in a statement. “We think behavioral science has an important role to play in preventing crashes and giving cities reliable solutions to improve road safety for all.”

San Francisco has embraced the Vision Zero or Safe System approach to roadway design that takes human error into account, first put into effect in Sweden in the 1990s. The goal is to eliminate all road deaths and serious injuries globally.

The education campaign included working with community-based organizations. Food delivery, virtual bike rides, and youth poster contests were among the methods used to maximize outreach to raise awareness about traffic safety.

“We are excited about the results of the project that will only move us forward towards eliminating the danger of left turns and making the streets safer for pedestrians, bikers, motorcyclists, and drivers,” Anni Chung, president & chief executive of Self-Help for the Elderly, said in a statement.

 To learn more about San Francisco’s Vision Zero initiative, click here and here. To find out more about the Safer Intersections Project, click here and here.