Davide D'Amico / Flickr

The data-driven solution was part marketing, part enforcement, and part community outreach.

Along with an increasing number of cities around the country, San Francisco has a “Vision Zero” plan to make its streets safer for pedestrians. The initiative’s near-term goal is to reduce deaths and serious injuries by 50 percent by 2021, and in this tech-dominated town, a big part of the strategy for doing that involves data—improving the quality of information on pedestrian injuries and fatalities, analyzing those numbers, and “using data to inform better public policy.”

A new study out this month from the city’s Department of Public Health and Municipal Transportation Agency gives you some idea of how data-driven policy analysis and implementation might work in practice. Officials looked at whether or not various interventions succeeded in getting drivers to yield to pedestrians at intersections. That’s important for safety, as the report notes, since “64 percent of all collisions between people walking and driving are ‘driver at fault.’ ”

The 43-week study looked at the effect that various tactics had on driver behavior at four of the most dangerous intersections in the city. Various measures were deployed in phases and in different combinations over the study period.

There was a publicity campaign with bus ads and billboards in the streets leading up to the intersections reading: “It Stops Here: Pedestrians have Right of Way.” In some crosswalks there was increased enforcement of the law that requires drivers to yield to pedestrians as well. And there was grassroots outreach, such as pamphlet distribution and meetings coordinated with community groups. For comparison, researchers looked at four control intersections without any interventions.

They found a 3- to 4-percent increase in drivers yielding to people on foot at intersections where the intervention tactics had been deployed. In contrast, the number of drivers yielding at the control sites actually fell.

While 3-to-4 percent may not sound like a big increase in compliance, the potential effect of widespread interventions looks meaningful when you scale it up. Researchers estimate that across the city, at intersections where a high rate of pedestrian injuries and fatalities occur, a 3-to-4 percent improvement would translate to 419 more drivers yielding per hour at peak commute times.

“This could result in hundreds of avoided collisions, some of which might have caused injuries or deaths,” Ed Reiskin of the Municipal Transportation Agency told SFGate. In 2014, by the city’s count, 96 people on foot were killed or severely injured in traffic crashes. That number exceeded the official goal of 82.

Injuries caused by crashes may affect more people than the tally of past years would indicate. Another recent study from the city’s Vision Zero team suggests that the number of traffic injuries is dramatically underestimated by the San Francisco Police Department, which has been the source of official figures. The study used hospital records to identify 515 patients admitted for severe traffic injuries over a 12-month period beginning in April 2014. SFPD records only reflected 200 injuries during that time—an underestimation of nearly 60 percent. Possible explanations for the low count include the fact that police officers are not trained medical personnel and that some injuries occur outside of city police jurisdiction (for instance, on state highways).

More data and better data are clearly still necessary. Just as important, once it’s gathered, the city has to commit to acting on the results.

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