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20 mph Zones
20 mph zones are European neighborhood areas where vehicle speeds are limited to 20 mph, primarily to protect against child pedestrian injuries. London Mayor Ken Livingstone made the expansion of 20 mph zones a platform in his unsuccessful 2008 reelection campaign.[1]
Effectiveness
A study by the British Transport Research Laboratory of 20 mph zones across Europe found they reduced child pedestrian crashes by two-thirds, and bicycle crashes by 29%.[2] The Department for Transport recommends that newly applied 20 mph zones include traffic calming devices if the 85th percentile speed (the maximum speed at which 85% of traffic is traveling) is 27 mph or higher. Otherwise, drivers are unlikely to obey the speed limit without strict, consistent police enforcement - the sort few cities can afford.[3]
Child Crash Prevention a Public Health Issue
Traffic crashes are recognized as a major pediatric health issue worldwide, but most interventions are applied to children travelling as passengers in cars. Examples are infant and child carseat laws, and prohibitions against children riding as passengers in front seats where air bags are installed. In the U.S., virtually no physical protections are provided for children as pedestrians and bicyclists, outside of signage and specially marked crosswalks in school zones.
In July 2008, the British Medical Association called for the application of 20 mph zones throughout residential neighborhoods, not just in the vicinity of schools, where they are commonly applied.[4] Stockport public health director Dr. Stphen Watkins stated that "a child hit at 20mph has a 5% chance of dying compared to 50% at 30mph." He noted the differnce between a two mile journey at 20mph and a two mile journey at 40 mph was just three minutes. "We are killing our children for the sake of a couple of minutes," he said.
20 mph Zones Improve the Economy
The UK study of best traffic practices across the Europe and the U.K. concluded that 20 mph streets also increased pedestrian activity, bicycling, a sense of safety among residents, and economic activity. The study cited evidence from the city of Horsham, U.K., where 20 mph speed limits, along with a bypass road, public arts, gardens, and other pedestrian amenities have lead to the opening of new shops and restaurants, and a higher level of overall eoconomic activity.[2]
U.S. Implementation
No known U.S. jurisdiction has implemented 20 mph zones. However, the non-profit PedNet Coalition[5] in Columbia, Missouri, sought to convince its city council to do so during 2009. For decades, city traffic engineers had refused to post lower speed limits, stating that such signs are ineffective. Seeking to show a 20 mph zone could be achieved, the PedNet group teamed with academic researchers and volunteers to conduct an education campaign in a selected neighborhood, and then installed special signs to limit speeding on residential streets. The tactic worked, and the city has subsequently begun work on an ordinance to lower residential street speed limits to 25 mph (rather than 20 mph).
ALSO ON THE LIVABLE STREETS NETWORK
REFERENCES
Each source is referred to by the same number every time it is cited. Please keep citation style consistent.
[1] Livingstone launches 20mph traffic plan. The Guardian, April 17, 2008.
[2] Study of European Best Practice in the Delivery of Integrated Transport: Report on Stage 3 - Transferability. Reports. UK Commission for Integrated Transport.
[3] 20 mph speed limits and zones: design advice. UK Department for Transport.
[4] Doctors support more 20mph zones. BBC News, July 9, 2008.
[5] PedNet Coalition, Columbia, Missouri. 2009. Columbia will lower residential speed limit to 25. Latest News.
PICTURE REFERENCES
Pictures are cited in the order they appear above. Please keep citation style consistent.
[1] 20 mph sign, Photo courtesy U.K. Department for Transport, subject to copyright terms.
[2] Children create their own 20 mph legend. Photo by greensambaman via Flickr.
