Techniques and Devices for Slowing Down Traffic (Traffic Calming Explained)

speed tableTraffic calming is changing a road to lower the speeds vehicles are driving, reduce the volume of traffic using the road, divert cut-through traffic or a combination both.  This is almost always done after concerned residents convince the municipal staff or political leaders there’s a problem on the existing road.  However, traffic calming treatments can also be built into roads in new subdivisions or existing roads that are being reconstructed.  In fact, roads within neighborhoods should almost always be studied for potential traffic calming treatments when street reconstruction projects are being designed.

Some treatments are more effective than others.  Sharp speed humps placed every few hundred feet are the most effective at slowing vehicles down while narrowing the road or raising a whole intersection up do very little to speeds.  Closing off a road so vehicles can’t cut through the neighborhood can be very effective at reducing traffic on the road while putting in a traffic circle won’t change driver patterns.

Typical traffic calming treatments try to divert motorists or slow them down by:

  1. Building vertical impediments in the road that will make driving too fast uncomfortable.
  2. Building shifts in the road that will force drivers to turn their vehicle, which will force them to drive slower.
  3. Narrowing the road so it is less comfortable to drive on.
  4. Closing the through road partially or fully.

Traffic calming treatments are often big changes for the neighbors along the streets.  The following process is recommended if a city is going to consider traffic calming projects:

  1. Require a neighborhood petition.
  2. Hold a series of public meetings for the neighborhood (and adjacent neighborhoods).
  3. Use paint, traffic cones, barrels, and other temporary means of installing the chosen treatments to test their effectiveness and neighborhood acceptance.
  4. If test goes well, install the measures permanently.

The input of the neighborhood, and adjacent neighborhoods, is crucial to the process.  The residents along the street will drive through the treatments several times a day and many of them may not like having to slow down or the noise associated with some of the traffic calming measures.  Also, pushing traffic over a street may be great for the residents living along the newly quiet street but just shifting the traffic volumes over doesn’t solve the big picture problem.


  • Can be costly
  • Potential, local community opposition
  • Reduced accessibility for local residents/commuters
  • Greater drive time/accessibility for semi-trucks and emergency vehicles (typically not appropriate in industrial areas or areas with high commercial access)
  • Limited to local streets or minor collectors
  • Not appropriate for busy roads (typically 4,000 vehicles per day is the cutoff)
  • Posted speed limit should be 30 mph or less
  • Typically for two-lane, two-way roadways

 Standard Traffic Calming Measures

  • Center Islands
  • Chicanes
  • Chokers
  • Diverters/Diagonal Barriers
  • Full Closures
  • Half Closures
  • Median Barriers
  • Neckdowns
  • Raised Crosswalks
  • Raised Intersections
  • Realigned Intersections
  • Reduced Intersection Turning Radius
  • Roundabouts
  • Speed Humps
  • Speed Tables
  • Textured Pavement
  • Traffic Circles


  1. Fehr & Peers (very good description of the different treatments available)

  1. Pennsylvania’s Traffic Calming Handbook’s%20Traffic%20Calming%20Handbook.pdf

  1. Institute of Transportation Engineers Traffic Calming Measures

  1. Federal Highway Administration Traffic Calming

  1. Seattle’s Traffic Calming Policy

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