Traffic Calming 101

In an earlier blog, we discussed some possible ways that Vision Zero may affect DC streets. Traffic calming is one of the tools for making streets safer for our most vulnerable users, like pedestrians, bicyclists, children, the elderly, and the mobility-impaired. Our roads are designed by traffic engineers. They tend to use the same standards that they use to design highways, even though neighborhood roads are used by a variety of users. When roads are “overbuilt” (ie: have more lanes than necessary, or wider lanes) they send signals to drivers that it’s okay to drive much faster than the posted speed limit. This is a design problem that can be addressed by the traffic calming measures discussed below. According to a report by the AAA Foundation for Traffic Safety, reducing vehicle speeds, also called “traffic calming,” makes a big difference in serious injuries and traffic fatalities. When a person is struck by a car traveling at 15 mph, the risk of death is less than 5%. At 25 mph, the risk of death more than doubles to 12%. And if a person is struck by a car traveling at 45mp, the risk of death is 60%! Slowing down traffic can greatly reduce the likelihood of death or serious injury for vulnerable road users. According to the Institute of Transportation Engineers, traffic calming is the combination of mainly physical measures that reduce the negative effects of motor vehicle use, alter driver behavior and improve conditions for non-motorized street users. Traffic calming is the deliberate slowing down of traffic through neighborhoods by building speed bumps or other obstructions. Traffic calming helps to reduce crashes and increases the safety and convenience of pedestrians and other non-motorized vehicles. Neighborhood Streets Network noted traffic calming measures can also give children more space to play, decrease noise pollution and improve the scenery.   This week, I’ll discuss some traffic calming measures suggested by the Project for Public Spaces you have probably seen in and around DC.

Road Diet

road diet In road diet, planners and engineers reduce the number of lanes, or width of existing lanes, on the street. This is usually done by creating a separate space for pedestrians and bicyclists to travel. Road diets help reduce crashes by separating bicyclists from cars with physical barriers, making everyone’s commute better. To learn more, check out this 2 minute video, which shows how planners can redesign a roadway.

Protected Bike Lanes

15th St. protected bike lane extension Protected bike lanes visually reduce the width of the roads which can reduce drivers’ speed and separate bicyclists from cars by using curbs, planters, or posts.  Protected bike lanes increase safety for bicyclists and encourage new riders to travel for shorter trips, which reduces traffic on the roadways.  

Curb Extensions

A curb extension in Montreal.

A curb extension in Montreal. Photo by Gerald Fittipaldi on Flickr.

Curb extensions physically and visually narrow the roadway without reducing the roadway capacity.  Curb extensions force drivers to be more attentive and drive closer to the speed limit since they lower the design speed of a road. Curb extensions increase pedestrian visibility while decreasing the amount of time it takes to cross the roadway.


roundabouts-1 Roundabouts are large, raised, circular islands at major intersections. Because the road narrows as a cars approach a roundabout, drivers tend to slow down. Roundabouts help to calm traffic by creating a steady flow of traffic. Since all drivers are traveling in the same direction and at a slower speed, crashes are less severe. Roundabouts are also safer for pedestrians and bicyclists because they only have to cross traffic coming in one direction and the distance is shorter than a typical intersection. These are just a few of the traffic calming measures that can be used in a city. They each help slow down drivers, which can reduce traffic fatalities and serious injuries. If you would like to learn more about how you can get involved in reducing traffic fatalities and serious injuries, join us for our community workshop: Sunday, November 20th 1pm- 4pm Dorothy Height Library 3935 Benning Rd. NE Washington,  D.C.  20019