Descriptive Title: Percent of drivers exceeding the speed limit by 5 miles per hour or more
Geographic Unit of Analysis: Street segment and planning neighborhood
|Percent of drivers exceeding speed limit by 5mph or more, on surveyed streets (2004-2009)|
|Neighborhood||Total Road Miles in Neighborhood||Surveyed Road Miles with Speed Data (%)||25 mph Streets, Avg. % Exceeding Speed Limit by 5 mph or more||All Measured Streets, Avg. % Exceeding Speed Limit by 5 mph or more|
|Financial District/South Beach||24||5%||73%||35%|
|Golden Gate Park||20||14%||47%||38%|
|South of Market||42||7%||24%||12%|
|West of Twin Peaks||47||8%||13%||14%|
Vehicle speed is a primary contributing factor to the severity of injuries suffered by pedestrians, cyclists, drivers and passengers in traffic collisions – with higher speeds allowing for less driver reaction time and increased force when collisions occur.a Vehicle speed has particularly profound impacts on more vulnerable road users, including pedestrians and cyclists. Small increases in impact speed translate into large increases in fatality risks – for example, it has been estimated that the risk of pedestrian fatality is six times that at 30 mph relative to 20 mph.b Reducing vehicle speed is thus a priority focus of international initiatives to improve road safety.c Given the correlation between vehicle speed and injury severity, there is a need for targeted speed management measures to ensure speed limit compliance such as engineering and enforcement efforts including the consideration of automated speed enforcement which has effectively reduced urban traffic speeds in other countries.d Though posted speed limit signs inform drivers of the speed, roadways can be designed with traffic calming improvements to alter driving behavior to drive slower, while also encouraging safety and awareness of other road users.e
On average, 18% of drivers exceeded the speed limit by 5 mph or more on the San Francisco streets surveyed, ranging from an average of 10% in the Western Addition to 60% in Chinatown. Neighborhoods with higher averages of drivers exceeding the speed limit on 25 mph streets by 5 mph or more include the Financial District (73%), Mission Bay (61%), and Chinatown (60%).
Speed compliance data was collected from 2004 to 2009 by the San Francisco Municipal Transportation Agency (SFMTA) on 57.8 miles of San Francisco streets (approximately 5% of San Francisco’s street length) with speed limits of 25, 30 and 35 miles per hour (mph). The data reflects the proportion of drivers who exceed the speed limit by 5 mph per speed limit. An average of the proportion of drivers who exceed the speed limit by 5mph per neighborhood and citywide was calculated for each of the speed limits, as well as for the average of the combination of all three speed limits. The combined proportion of drivers who exceed the speed limit per neighborhood was used to create the map (above) in ESRIs ArcGIS 10.0 software.
Approximately 5% of San Francisco streets (57.8 miles) had speed data collected from 2004 to 2009. While some neighborhoods had up to 14% of their street segments surveyed (Golden Gate Park), others had little to no speed survey data collected and were thus excluded from the combined analysis due to small sample size (neighborhoods with <4% of street length surveyed were excluded; see map and table). While most of the speed data was collected as a part of routine SFMTA operations, some data was also collected on an as-needed basis including in response to speed complaints.
Not all streets in San Francisco have posted speed limits. The de facto speed limit on San Francisco streets is 25 mph; an exception is alleys narrower than 25 feet which have a de facto speed limit of 15 mph.
The neighborhood-level categories in the map (above) depict the average proportion of vehicles exceeding the speed limit on all streets with measured speed data (includes street with 25 mph, 30 mph, and/or 35 mph speed limits). The table further illustrates differences in the average proportion of vehicles exceeding the speed limit on 25 mph streets, which comprise the largest proportion of San Francisco’s street network.
Vehicle speed data was collected the San Francisco Municipal Transportation Agency (SFMTA) from 2004 to 2009 and consists of both pneumatic tube and radar measurements. Data entry and mapping conducted by City and County of San Francisco, Department of Public Health, Environmental Health Section using ArcGIS software.
Map data is presented at the level of the planning neighborhood.
Table data is presented by planning neighborhood.
Detailed information regarding census data, geographic units of analysis, their definitions, and their boundaries can be found at the following links:
Ewing R, Dumbaugh E. 2009. The Built Environment and Traffic Safety : A Review of Empirical Evidence. Journal of Planning Literature 23: 347-367.
Richards, D.C., 2010. Relationship between Speed and Risk of Fatal Injury: Pedestrians and Car Occupants. Transportation Research Laboratory. Road Safety Web Publication No. 16. Department for Transport: London, UK.
WHO (World Health Organization), 2011a. United Nations Road Safety Collaboration: World unites to halt death and injury on the road. Available from: http://www.who.int/roadsafety/en.
GRSP (Global Road Safety Partnership), 2008. Speed management: A road safety manual for decision-makers and practitioners. Available from: http://whqlibdoc.who.int/publications/2008/9782940395040_eng.pdf.
Policy Link. 2010. Healthy, Equitable Transportation Polcy: Recommendations and Research. www.convergencepartnership.org/transportationhealthandequity