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What Is Traffic Calming?

Read Time: 4 minutes

Traffic calming is a set of design interventions aimed at slowing or diverting car traffic to reduce the chance of crashes and improve safety for all road users.


SLOW painted on asphalt street

Semmick Photo / Slow

First developed in Germany as “vekehrsberuhigung,” traffic calming refers to a system of road safety interventions based on the idea that streets are not just a conduit for moving vehicles at the fastest rate possible. The term describes a set of design guidelines and devices that are designed to discourage speeding and other dangerous driving behaviors to make streets safer for all users, including those on foot.

Traffic calming aims to slow and, in some cases, divert traffic without banning it entirely, putting cars on a somewhat more equal footing with other transportation modes and reducing the chance of crashes, severe injuries, and deaths. Traffic calming projects also offer the opportunity for landscaping, seating, and other amenities that can break up monotonous blocks, reduce air pollution, and increase opportunities for social interaction.

Because they are low-cost and easy to install, some traffic calming strategies have become popular interventions in the tactical urbanism movement, which promotes short-term, often citizen-led “pop-up” projects that activate public space and can demonstrate the benefits to local stakeholders and officials. As an example, some groups, like Crosswalk Collective LA in Los Angeles, have taken to painting their own crosswalks at dangerous intersections and crossings to alert drivers to the presence of pedestrians, circumventing official channels. While projects like this can create conflict between activist groups and city agencies, they can also foster discussion of dangerous conditions and prompt action at the government level.

Traffic Calming Strategies and Devices

Traffic calming measures fall into several categories: horizontal deflections that change an otherwise straight roadway; vertical deflections that change roadway height; street width reductions; and routing restrictions. These are often inexpensive, quick-build interventions that reduce vehicle speeds, improve pedestrian safety, and/or reduce cut-through traffic. These include:

  • Pedestrian crossing islands, raised medians, and curb bulb-outs to reduce the distance pedestrians must cross and discourage speeding.
  • Raised crosswalks that slow drivers and make crosswalks more visible.
  • Road humps, speed tables, rumble strips, and other physical means of slowing cars. These devices can be designed in ways that can accommodate emergency vehicles and bicycles.
  • Lateral shifts that realign an otherwise straight road by shifting travel lanes, causing drivers to slow. A chicane is a series of several lane shifts created by curb extensions or medians that force drivers to travel a curved path, slowing them down. This application is appropriate on low-speed streets and short blocks or mid-block sites.
  • Diagonal parking to increase driver awareness and use space more efficiently. On-street parking can be designed to slow traffic while providing more ample parking space.
  • Widened sidewalks and reduced traffic lanes to create space for non-car uses.
  • Roundabouts and traffic circles to improve the flow of traffic and reduce conflict points.
  • Bollards, diverters, or other barriers that limit traffic on local streets and guide traffic (e.g. a concrete island that only permits left turns) to make roadways safer for pedestrians and bikes.
  • Realigned intersections, also called modified intersections, are purposely reconfigured with skewed approaches, forcing cars to slow as they pass through. This measure is effective in T-intersections and other small streets.

Traffic calming measures often function best in combination with each other. The low cost and easy implementation of traffic calming measures also lets cities make immediate improvements while testing approaches at low risk and adjust programs accordingly. Making streets safer and more comfortable for people walking and biking can also boost public transit, as people are more likely to use transit when their route to the nearest stop is safe and easy to navigate.

One of the most prominent examples of comprehensive traffic calming strategies is the Dutch woonerf. The woonerf concept positions the street as a space for social interaction and a variety of uses aside from vehicle throughput. First developed in the 1960s in Delft, where residents replaced their streets with winding paths to divert traffic away from their neighborhoods, the woonerf famously blurs the line between pedestrian space and automobile space by removing curbs and has inspired successful street redesigns in the Netherlands and other European countries.

Roundabout on residential street
Roundabout
Median with landscaping and bike lane
Median with landscaping and bike lane
Curb bulb-outs at midblock crosswalk
Curb bulb-outs at midblock crosswalk
Speed hump
Speed hump
Traffic calming chicane on small street in UK
Lateral shift

Challenges and Obstacles

Traffic calming initiatives face a number of challenges and concerns, including traffic safety, impact on traffic flow and volume, uniformity of standards, liability issues, access to utilities, emergency vehicle and transit access, and impacts on bicycling and accessibility. As such, while traffic calming projects can be relatively low-cost, they require coordination with other departments and stakeholders to ensure that they can be integrated into existing infrastructure as seamlessly as possible. Small, temporary pilot projects or DIY installations can help gain support from local officials and residents and highlight the benefits of scaling up the project.

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