Traffic calming is an umbrella term used for strategies to decrease auto speeds and cut-through motor vehicle traffic, typically on local roads or arterials in downtown, urban settings. Traffic calming measures require drivers to slow their vehicles to acceptable speeds in order to avoid physical or psychological discomfort. Despite becoming more popular and accepted, there are a variety of issues surround traffic calming techniques that require careful attention during the planning and construction phase.
Traffic calming measures can either be operational adjustments to the road system or physical installations. Operational adjustments include increased or better signage to alert drivers to speed limits; pavement markings to decrease lane widths; and establishing a series of multi-way stop signs at previously unmarked intersections. Operational adjustments are cheap, quick and usually politically safe; however, they require enforcement and may not yield the desired results.
Physical traffic calming installments come in three types. Horizontal diversion, such as bulb-outs, chicanes and curb extensions either hinder the vehicle’s ability to move in a straight line or squeeze lane widths to force a slower speed for comfortable travel. Vertical deflection includes speed bumps, speed humps and raised sidewalks, all of which also require slow vehicle speeds. Finally, physical obstruction can divert unwanted traffic around the affected neighborhoods, or provide an obstacle requiring the motorist to slow down in order to safely bypass it. These include diverters, right-in/right-out islands and traffic circles. Physical installations tend to have better results but are more costly, can have unforeseen consequences and can be politically contentious.
Traffic calming measures can promote non-auto transportation modes not only by increasing bike/ped safety, but also by providing platforms for bike/ped facilities. For example, bulb-outs can serve to not only restrict lane widths that slow cars down, but also to decrease crossing distance for pedestrians. Another example is to use the plateau surface of a speed hump as a raised crosswalk.
In Pennsylvania, liquid fuels tax, state or federal funds can only be used for traffic calming measures if a proscribed process is followed. This process includes the formation of a municipal Local Traffic Advisory Committee, the commissioning of a background study to determine what types of traffic calming measures, if any, are appropriate, public surveys/hearings and evaluation of the installed facilities. This process is good practice regardless of the funding source.
- Enhanced neighborhood safety and quality of life
- Decreased vehicle noise in residential areas
- Promotion of alternative transportation modes
- Considerable costs associated with some installation types
- Lengthy study and approval process for installations funded by liquid fuel tax, state or federal sources
- Unforeseen consequences of pushing traffic into other neighborhoods
- Pushback from unsupportive citizens
- Engage community members early in the process
- Consult with PennDOT district engineers for design guidelines
- Identify funding sources and project priorities within the framework of the larger municipal budget
- The traffic calming section of the PA Land Trust Association website includes examples in Lemoyne and Carlisle boroughs in Cumberland County.