“Any [cyclist] or pedestrian death or serious injury is one too many… By looking out for each other and by driving more slowly and carefully, we can make a big difference in improving safety in San Francisco.”
– Ed Lee, Mayor of San Francisco
To measure the success of the Safer Market Street project, Zendrive conducted an analysis of the impact of the policy. We collected data before and after certain features, like turn restrictions, went into effect August 11, 2015. Using our data and technology, we examined over 100,000 trips and 2,000 drivers from August 2015 to February 2016.
“It’s encouraging to see the private sector focus attention on solving city transportation challenges,” said Paul Rose, a spokesman for the SFMTA. “To have outside organizations like Zendrive take a look at how we’re making our streets as safe as possible is beneficial to everyone who uses these roadways.”
“Collecting and using data wisely are core to reaching Vision Zero, so it’s tremendously valuable to have Zendrive’s analytical power to assess how road safety improvements impact people’s driving behavior and safety. Now, knowing this is possible, it’s critical that local leaders harness these public-private partnerships to develop strong data-driven policies and street designs that will save lives."
– Leah Shahum, Director of the national National Vision Zero Network
Cyclists and pedestrians in San Francisco have more than enough to worry about. From steep hills to crooked streets to the rolling fog we endearingly call Karl, there are a multitude of battles for road warriors to win. Unfortunately, of the 30 traffic fatalities and 200 serious injuries estimated per year in San Francisco, most involve cyclists and pedestrians.
Following our previous study, we were excited to see the city of San Francisco implement the Safer Market Street project. This project is one of 24 projects identified by the SFMTA to address fatalities along high-injury corridors in the city. According to the SFMTA and SFCTA, a busy intersection on Market Street at peak hour can see up to 10,000 pedestrians, 300 cyclists and 1,000 drivers (1).
“As important and central a street as Market Street is for the city, it is also a place where a lot of people are being injured and killed in collisions… It’s home to four of the top 20 injury intersections in the city.”
– Ed Reiskin, Director of SFMTA
Traffic fatalities are such rare events that variance can be due to multiple extraneous factors, such as seasonality. A better measure of safety improvement is driver behavior change, and in particular, changes in risky driving behavior. Using sensors on a smartphone, Zendrive monitors risky driving behavior in real time.
Our technology tracks events such as hard braking and speeding – robust measures of collision risk (2).
One of the long term goals of the policy is to divert traffic off of Market Street through features like turn restrictions. We found that over the course of 6 months, total traffic volume dropped by 22% along the impacted corridor.*
The policy reduced the number of private vehicles on Market Street and simplified turn movements. The outcome is a lowered risk of collisions between pedestrians, cyclists and drivers at high-injury intersections along Market Street.
Another goal the city outlined is to make the corridor safer. We found that within weeks after the implementation of Safer Market Street, drivers were less likely to engage in aggressive driving behavior, such as hard braking and speeding.
After 1 month, we observed 39% reduction in speeding and 15% reduction in hard braking. Over the course of 6 months, the improvements to the impacted corridor are even more striking – 72% reduction in speeding and 37% reduction in hard braking.
The decrease in hard braking and speeding is a leading indicator of reduced collision risk along the corridor. We hypothesize that simplified intersections results in smoother traffic flow. This helps drivers focus more on the road, signage like speed limits and cyclists and pedestrians around them. It also results in drivers needing to start and stop less frequently, which means less lurching and hard braking.
Additionally, we found that the positive impact was not restricted to Market Street. Our data showed there was a positive ripple effect along neighboring Mission Street one block down. Over the course of 6 months, we observed 56% reduction in speeding and 47% reduction in hard braking along the Mission Street corridor parallel to the impacted Market Street corridor.*
This positive side effect is likely the result of a network effect. After a change in driving behavior on one street, driving behavior is expected to change on neighboring streets within the network (3). As drivers improve their driving behavior on Market Street, the network effect means they continue to drive safely as they navigate to adjacent roads like Mission Street.
In addition, there is a common perception among drivers after changes in transit policy that there is more monitoring by enforcement in areas surrounding impacted roads. Studies show that people who are aware of being observed are more likely to improve their behavior (4).
The Safer Market Street improvements reduced traffic and made driving through formerly complicated intersections more straightforward. These better and simpler road conditions allow drivers to pay more attention to the traffic around them. This has resulted in less speeding and hard braking, and safer roads for drivers, passengers, cyclists and pedestrians.
Furthermore, the Safer Market Street project has spread its positive impact to Mission Street and likely beyond, taking San Francisco one step closer to realizing its Vision Zero goal.
*Traffic volumes along the impacted Market Street corridor were normalized to account for seasonality and fluctuations in overall city traffic volume. All percentage decreases in speeding and hard braking were normalized to account for the reduction in total traffic volume along the corridor.
(1) SFMTA and SF County Transportation Authority Technology, Data & Analysis Team, 2016.
(2) U.S. Department of Transportation National Highway Traffic Safety, 2005, Elander, 1993 and Wahlberg, 2007
(3) Zhu and Levinson, 2009
(4) Wouters and Bos, 2000