Traffic Calming Explained

Traffic calming is generally defined as the deliberate slowing of vehicles in residential areas through physical or other obstructions. More generally, we refer to it as changing a road in an attempt to lower vehicle speeds, reduce traffic volumes, divert cut-through traffic, or some combination therein. Traffic calming is almost always considered after concerned residents convince the municipal staff or political leaders there’s a problem on the existing road. However, traffic calming treatments and techniques can and should be built into new roads while planning subdivisions or designed into existing roads during reconstruction projects.

Some treatments are more effective than others. Sharp speed humps placed every few hundred feet are more effective at slowing speeds compared to road narrowing or raised intersections. Closing off a road so vehicles can’t “cut-through” a neighborhood can be very effective at reducing traffic on the road while a traffic circle may not change driver patterns.

Typical traffic calming treatments are sub-divided into four categories:

1. Vertical impediments; designed to make fast driving uncomfortable.
2. Horizontal impediments; designed to make a driver turn the wheel and reduce the sight lines of unending pavement, which usually results in slower speeds.
3. Road narrowing; via striping, parking, or curb to reduce the drive lane widths, which generally causes drivers to slow down.
4. Closing the through road partially or fully to disrupt travel patterns.

Within these four sub-categories are numerous options. Here’s our list of the more standard traffic calming measures:

+ Angled Slow Points
+ Center Islands
+ Chicanes
+ Chokers
+ Diverters/Diagonal Barriers
+ Full Closures
+ Half Closures
+ Intersection Neckdowns/Mid-Block Bulb-Outs
+ Median Barriers
+ Neckdowns
+ Raised Crosswalks
+ Raised Intersections
+ Realigned Intersections
+ Reduced Intersection Turning Radius
+ Roundabouts
+ Speed Humps
+ Speed Tables
+ Striped Bicycle Lanes to Narrow the Drive Lanes
+ Textured Pavement
+ Traffic Circles

Although these treatments can help reduce speeds and volumes in many situations, there are limitations to be considered, including:

+ Can be costly to install, and remove if necessary
+ Potential, local community opposition from other streets (where traffic may shift) or residents who don’t want the impacts on their travel route
+ 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

Traffic calming measures should be carefully studied before implementation. Ideally, the process to install should include public input and meetings to discuss as well as a temporary installation (using traffic cones, barrels, etc.) to test before permanent installation. This will help avoid the limitations suggested and ensure the issues are solved with acceptance by neighbors.

Want to learn more? Here are some of the best resources we have found.

+ Fehr & Peers (very good description of the different treatments available)
Pennsylvania’s Traffic Calming Handbook
+ Institute of Transportation Engineers Traffic Calming Measures
+ Federal Highway Administration Traffic Calming
Seattle’s Traffic Calming Policy