Traffic Calming

Background

As the number of cars being driven grows, there is an increasing clash between motorists looking for unclogged short cuts and residents who want their neighborhood streets free from speeding commuters. With 6,000 pedestrian/car fatalities annually, where to route traffic and how to maintain safe residential streets is a concern for many communities. Simply slowing, if not eliminating, traffic helps: Studies show that a pedestrian hit by a car going 35 mph or faster has an 85 percent likelihood of being killed. They have an 85 percent chance of surviving when cars are moving 18 mph or slower (1). Many communities are turning to traffic calming techniques to bring the situation under control.

Policies

1. Reroute through traffic from residential streets to arterial streets.
   
   Sometimes drastic measures are required to keep traffic on intended routes. In San Francisco, CA, more than 4,000 vehicles per day used a one-block residential street as a short cut to a freeway onramp. To keep the traffic on the main route to the onramp, officials placed steel barriers at one end of the street and movable wooden barriers at the other – discouraging commuters but still allowing residents access (2).
   
   
2. Build humps, bends and traffic circles on neighborhood streets to slow or reduce traffic.
   
   Traffic engineers have a variety of measures at hand. Traffic circles force drivers to reduce speed as they maneuver through intersections. Bulb-outs are curbs that jut into the street to narrow the roadway and discourage speeders. Speed tables are flat, raised surfaces of bright red brick that force drivers to slow down. Street parking or landscaping can be alternated from one side of the street to another so the driver sees a zigzagged road rather than a clear straight path, another discouragement to speed (3).
   
   

Effectiveness Data

Many cities have embraced traffic calming measures recently (Sacramento, Roseville and Davis in California's valley) but others have been practicing the techniques for decades: Berkeley, Seattle and Portland, for instance (4). Seattle studied 15 intersections before and after construction of traffic calming devices and found that total collisions dropped from 33 per year to three. In Europe, where traffic planners have more than 30 years' experience implementing traffic calming, numerous evaluations have shown a reduction in crashes, injuries and fatalities (5).

Contacts

Daryl R. Grigsby, Director of Seattle Transportation
Phone: 206-684-5000
E-mail: daryl.grigsby@ci.seattle.wa.us
Web site: http://www.ci.seattle.wa.us/td

Marty Hanneman, City Traffic Engineer
Sacramento Public Works Department
Phone: 916-264-5307
E-mail: mhannema@sacto.org
Web site: http://www.pwsacramento.com/

References

1. Communities Finding Ways to Brake Zip-through Drivers. USA Today, May 2, 1997. :24A.
   
   
2. Neighborhood Beats the Rush of Traffic on Tiffany Avenue. San Francisco Chronicle, February 18, 1997. :C1.
   
   
3. Lewis D. The Do's and Don'ts of Traffic Calming. Traffic Safety, March/April 1998. :16.
   
   
4. Cities Increasingly Try to Slow Down, Divert Cars. The Sacramento Bee, July 5, 1998. :A1.
   
   
5. Pedestrian and Bicyclist Safety and Accommodation. National Highway Traffic Safety Administration, U.S. Department of Transportation. FWHA-HI-96-028. :73.
   
   

Acknowledgements

Kathleen Beasley, Editor

Dale Danley, M.P.H., Writer