Speed, Safety, and Traffic Calming

There are a number of sources supporting the reduction of speed and the increase in safety produced by traffic calming: 

 "The superior safety of traffic calmed streets has been consistently proven in many countries over the world, especially because of the reduction in motor vehicle speeds. With slower speeds two important things happen. First, drivers can stop their cars in shorter distances. Second, drivers' fields of vision expand at slower speeds. In other words, they can see more, especially to the sides of the streets. The combination of these two factors results in drivers being able to avoid collisions more often than on non-traffic calmed streets. If there is a collision on a traffic calmed street, experience has shown that the damage to people and property is also reduced due to the lower speed." (1) 
Studies in the Netherlands show that "against the background of studies of a total of 44 redesigned roads, the Traffic Safety Research Council has found a reduction of the frequency of accidents of 72% and a reduction of serious injuries of 78%. These very positive results are confirmed by other studies for example in Germany and France." (2)

“Motorists driving at 25 mph or faster have difficulty perceiving that a pedestrian is ready to cross a street, deciding to slow down, and actually doing so. The normal driver usually decides to speed up, assuming that another car will stop.”
85 British case studies on traffic calmed streets with volumes of up to 18,000 vehicles show the vast majority resulted in speed and/or accident reductions of over 30%. (3) 
A 1979 German analysis of the first 30 traffic calming projects the Federal Government had undertaken "showed that injuries had been reduced by 44% and serious accidents and deaths by 53% in the 30 areas." (4) 
In 1988, Mr. Monheim reported that "the German experiment had proved that traffic calming worked equally as well in low density areas as in high density areas." Accidents remained the same in number but fatalities were reduced by 43 - 53%, and injuries reduced by 60%. (5)
The Conservation Law Foundation of Boston provides a telling summary: (6)
"A wide pavement exerts a strong influence over a motorist. First, it puts someone in a car or truck at a greater distance from objects on either side. Looking at objects that are farther away creates the feeling that a vehicle is moving more slowly and prompts a motorist to compensate by speeding up. Second, by making the motorist survey a broad field in front of his vehicle, a wide pavement provides an assurance that he is in command of that field, which in turn induces him to increase his speed. In addition, when a wide pavement means more lanes, it leaves fewer vehicles in each lane and increases the distance between each vehicle, providing yet another inducement to go faster. Thus an urban arterial with three 11- or 12-foot travel lanes, or a broad two-lane residential street, can have a virtually irresistible effect. Even motorists who aren't inclined to drive fast creep up to highway speeds. Others seize the opportunity to floor it. ”
"Widening a road can of course affect the landscape - the "streetscape" in a city or town - as well as raise traffic speeds. Highway departments also propose cutting down trees, removing other vegetation, taking property by eminent domain, lowering hills, and straightening a road to create what they assume to be the necessary stopping sight distance. The stopping sight distance is the distance needed for a vehicle to come to a stop, taking into account the time in takes for a motorist to perceive and react to an event, brake, and bring the car to a halt.”
Sixteen percent of all people killed in motor vehicle accidents are pedestrians or bicyclists. These deaths are vastly out of proportion to the presence of pedestrians and bicyclists on the nation's streets and roads...Regardless of posted speed limits, motorists will drive faster when given 'safety cushion' of a wider road and greater sight distances. Higher design-speed roads have an insidious psychological effect on most motorists, prompting them to increase their speed unwittingly. When motorists drive faster, pedestrian accidents are both more likely and more serious. 
“The likelihood that a pedestrian will be hit increases at higher speeds because a motorist's ability to take in the surrounding environment is more limited. At a speed of 30 miles per hour, a motorist has a field of vision ('peripheral vision angle') spanning approximately 150 degrees, and will fix his or her vision about 1,000 feet ahead. At 60 miles per hour, the motorist's field of vision is reduced by two-thirds to 50 degrees, and the motorist will fix his vision at 2,000 feet.”
  • Ian Lockwood, Traffic Calming Engineer, presentation at Middleburg Community Center, December 4, 1995.
  • Reported in the Denmark Ministry of Transport, Road Directorate. An Improved Traffic Environment -- A Catalogue of Ideas, Danish Road Directorate, Road Data Laboratory, Roads Standards Division, Report 106, 1993. 
  • Traffic Calming in Practice, County Surveyors' Society, Assoc. Of London Borough Engineers and Surveyors, Assoc., of Metropolitan District Engineers, Assoc. Of Chief Technical Officers, the Department of Transport. Landor Publishing Ltd. London, 1994. 
  • Rolf Monheim, quoted from Traffic Calming: The Solution to Urban Traffic and a New Vision for Neighborhood Livability, published by CART (Citizens Advocating Responsible Transportation), Ashgrove, Australia, 1989; reprinted in the United States, with permission, by Sensible Transportation Options for People (STOP), Tigard, OR, 1993. 
  • Ibid. 
  • Take Back Your Streets, Conservation Law Foundation, Boston, 1995. Reprinted with permission
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