Traffic calming

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Signing indicating that a motorist is approaching traffic calming devices
A median island with a raised mid-block crosswalk
A curb extension at a mid-block crosswalk
A chicane on a one-lane road
A diverter replaces a four-leg intersection with two curves
The available turning radius has been reduced at this intersection
A motorist disregarding a directional closure (a two-lane roadway with one terminus converted to one-way access)
Two traffic calming measures: speed cushions (the two reddish pads in the road) and a curb extension (marked by the black posts and white stripes)

Traffic calming is a set of strategies used by urban planners and traffic engineers which aim to slow down or reduce traffic, thereby improving safety for pedestrians and bicyclists as well as improving the environment for residents. Calming measures are common in Australia and Europe (especially Northern Europe) but less so in North America.

Traffic calming was traditionally justified on the grounds of pedestrian safety and reduction of noise and local air pollution which are side effects of the traffic. However, streets have many 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.

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.[citation needed]

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.


[edit] Types of traffic-calming engineering measures

Traffic calming can include the following engineering measures:

  • Narrower traffic lanes — streets can be narrowed by extending the sidewalk, adding bollards or planters, or adding a bike lane or parking. Narrowing traffic lanes differs from other road treatments by making slower speeds seem more natural to drivers and less of an artificial imposition, as opposed to most other treatments used that physically force lower speeds or restrict route choice.
  • Speed bumps, sometimes split or offset in the middle to help emergency vehicles reduce delay
  • Speed humps, parabolic devices that are less aggressive than speed bumps and used on residential streets
  • Speed tables, long flat-topped speed humps that slow cars more gradually than humps
  • Speed cushions, a series of three small speed humps that slow cars down but allow emergency vehicles to straddle them so as not to slow response time
  • Chicanes, which create a horizontal deflection causing vehicles to slow as they would for a curve
  • Raised pedestrian crossings and raised intersection
  • Curb extensions (also called bulbouts) which narrow the width of the roadway at pedestrian crossings
  • Pedestrian refuges or small islands in the middle of the street
  • Median diverters to prevent left turns or through movements into a residential area
  • Changing the surface material or texture (for example, the selective use of brick or cobblestone)
  • Additional give way (yield) signs
  • Converting one-way streets into two-way streets
  • Chokers, which are curb extensions that narrow the roadway to a single lane at points[1]
  • Allowing parking on one or both sides of a street
  • Converting an intersection into a cul-de-sac or dead end
  • Boom barrier, restricting through traffic to authorised vehicles only.
  • Closing of streets to create pedestrian zones
  • Reducing speed limits near institutions such as schools and hospitals
  • Vehicle activated sign, signs which react with a message if they detect a vehicle exceeding a pre-determined speed.
  • Watchman, traffic calming system

[edit] Speed limits

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.[2] The Austrian city of Graz, which has achieved steady growth in cycling, has applied 30 km/h limits to 75% its streets since 1994[3]. 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.

Gatso speed camera

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.[4] 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.[5] 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.[6] Cycling has been declining in the UK in recent years.[7] 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.[8] 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.[9] 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.[10][11]

[edit] Recent trends in North America

Traffic calming has been successfully used for decades in cities across Europe. More recently, in response to growing numbers of traffic accidents and speeding problems[citation needed], 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.

[edit] Living street

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.

[edit] See also

[edit] External links

[edit] References

  1. ^ single lane chokerITE
  2. ^ Speed reduction, traffic calming or cycling facilities: a question of what best achieves the goals?, Michael Yeates, Convenor, Cyclists Urban Speed limit Taskforce, Bicycle Federation of Australia, Velomondial Conference Proceedings, Amsterdam 2000
  3. ^ The Graz traffic calming model and its consequences for cyclists, Manfred Hoenig, Department of transportation, City Council Graz, Velomondial Conference Proceedings, Amsterdam 2000
  4. ^ Enabling and encouraging people to cycle, John Franklin, Paper presented to the Cambridge Cycling Campaign AGM, 5 October 1999
  5. ^ How to enhance WALking and CYcliNG instead of shorter car trips and to make these modes safer, Deliverable D6 WALCYNG Contract No: UR-96-SC.099, Department of Traffic Planning and Engineering, University of Lund, Sweden 1999
  6. ^ Gary Cleland (2008-03-14). "\accessdate=2008-03-18 Speed cameras collect over £100m in fines". The Daily Telegraph (Telegraph Media Group). \accessdate=2008-03-18. 
  7. ^ "Cycling: Personal travel factsheet" (PDF). UK Department for Transport. January 2007. 
  8. ^ Learning from Hilden’s Successes, Rod King, Warrington Cycle Campaign, August 2004 (Accessed 2007-01-24)
  9. ^ Home Zones briefing sheet, Robert Huxford, Proceedings, Institution of Civil Engineers, Transport, 135, 45-46, February 1999
  10. ^ Road Narrowings and Pinch Points An Information Sheet, Galway Cycling Campaign, February 2001
  11. ^ Cyclists at Road Narrowings, by Howard Peel, The Bike Zone. (Accessed 2007-01-27)

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