Traffic calming is intended to slow or reduce motor-vehicle traffic in order to improve the living conditions for residents as well as to improve safety for pedestrians and cyclists. Urban planners and traffic engineers have many strategies for traffic calming. Such measures are common in Australia and Europe (especially Northern Europe), but less so in North America.
Traffic calming was originally justified on the grounds of pedestrian safety and reduction of noise and local air pollution which are side effects of the traffic. However, it is now recognized that streets have social and recreational functions which are severely impaired by car traffic. The Livable Streets study by Donald Appleyard (circa 1977) found that residents of streets with light traffic had, on average, three more friends and twice as many acquaintances as the people on streets with heavy traffic which were otherwise similar in dimensions, income, etc. For much of the twentieth century, streets were designed by engineers who were charged only with ensuring traffic flow and not with fostering the other functions of streets. The basis for traffic calming is broadening traffic engineering to include designing for these functions.
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There are 3 "E"s that traffic engineers refer to when discussing traffic calming: engineering, (community) education, and (police) enforcement. Because neighborhood traffic management studies have shown that often it is the residents themselves who are contributing to the perceived speeding problem within the neighborhood, it is stressed that the most effective traffic calming plans will entail all three components, and that engineering measures alone will not produce satisfactory results.
Engineering measures involve physically altering the road layout or appearance to actively, or passively slow traffic down. Measures include speed humps, chicanes, curb extensions, and living street and shared space type schemes. The town of Hilden in Germany has achieved a rate of 24% of trips being on two wheels, mainly via traffic calming and the use of 30 km/h (20 mph) zones.[1] As of 1999, the Netherlands had over 6000 woonerven where cyclists and pedestrians have legal priority over cars and where a motorised speed limit of "walking speed" applies.[2] However, some UK and Irish "traffic calming" schemes, particularly involving road narrowings, are viewed as extremely hostile and have been implicated directly in death and injury to cyclists.[3][4]
A number of visual changes to roads are being made to many streets to bring about more attentive driving, reduced speeds, reduced crashes, and greater tendency to yield to pedestrians. Visual traffic calming includes lane narrowings (9-10'), road diets (reduction in lanes), use of trees next to streets, on-street parking, and buildings placed in urban fashion close to streets.
Physical devices include speed humps, speed cushions, and speed tables, sized for the desired speed. Such measures slow cars to between 10 and 25 miles (15–40 km) per hour. Most devices are made of asphalt or concrete but rubber traffic calming products are emerging as an effective alternative with several advantages.
Traffic calming can include the following engineering measures:
Enforcement and education measures for traffic calming include:
Speed reduction has traditionally been attempted by the introduction of statutory speed limits. Traffic speeds of 30 km/h (20 mph) and lower are said to be more desirable on urban roads with mixed traffic.[6] The Austrian city of Graz, which has achieved steady growth in cycling, has applied 30 km/h limits to 75% its streets since 1994.[7] Zones where speeds are set at 30 kph (or 20 mph) are gaining popularity [8] as they are found to be effective at reducing crashes and increasing community cohesion. [9] Speed limits which are set below the speed that most motorists perceive to be reasonable for the given road require additional measures to improve compliance. Attempts to improve speed limit observance are usually by either education, enforcement or road engineering. Education can mean publicity campaigns or targeted road user training.
Speed limit Enforcement techniques include: direct police action, automated systems such as speed cameras or vehicle activated signs or traffic lights triggered by traffic exceeding a preset speed threshold. One cycling expert argues for placing direct restrictions on motor-vehicle speed and acceleration performance.[10] An EU report on promoting walking and cycling specifies as one of its top measures comprehensive camera-based speed control using mainly movable equipment at unexpected spots.[11] The Netherlands has an estimated 1,500 speed/red-light camera installations and has set a target for 30 km/h limits on 70% of urban roads. The UK has more than 6,000 speed-cameras, which raised more than £100 million in fines in 2006/07.[12]
Traffic calming has been successfully used for decades in cities across Europe. For example, a living street (sometimes known as Home zones or by the Dutch word woonerf, as the concept originated in the Netherlands) is a street in which the needs of car drivers are secondary to the needs of users of the street as a whole; traffic calming principles are integrated into their design.
More recently, in response to growing numbers of traffic accidents and speeding problems, cities across North America have begun creating traffic calming programs to improve safety and liveability on residential streets. Many municipalities create asphalt or concrete measures, although preformed rubber products that are easier to install and consistently meet standardized requirements are becoming increasingly popular.
A Cochrane Review of studies found that there is evidence to demonstrate the efficacy of traffic calming measures in reducing traffic-related injuries and may even reduce deaths. However, the review found that more evidence is needed to demonstrate its efficacy in low income countries.[13]
According to economic commentator and smart growth critic Randal O'Toole, the main goal of traffic calming is to increase congestion of motor traffic. He claims that some traffic calming measures such as reverting one way roads into two-way roads or creating "bump outs" have increased motor traffic congestion, resulted in more accidents and increased pedestrian fatalities.[14] According to Florida urban planner Dom Nozzi "[c]ongestion is a powerful disincentive for sprawl; sprawl that steamrolls outlying ecosystems. With congestion, the sprawl market wither."[15]