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SPEED LIMIT MISCONCEPTIONS

When traffic problems occur concerned citizens frequently ask why we don’t lower the speed limit. There are widely held misconceptions that speed limit signs will slow the speed of traffic, reduce accidents and increase safety. Most drivers drive at a speed which they consider to be appropriate, regardless of the posted speed limit. "Before and after" studies have shown that there are no significant changes in average vehicle speeds following the posting of new or revised speed limits. Furthermore, research has found no direct relationship between speed limits and accident frequency.

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Potential Impacts:

* no effect on access
* speeds are reduced, but usually to a higher crossing speed than at speed humps (typically between 25 and 27 miles per hour)
* traffic volumes have been reduced on average by 12 percent depending on alternative routes available
* collisions have been reduced on average by 45 percent on treated streets (not adjusted for traffic diversion)
* reported to increase pedestrian visibility and likelihood that driver yields to pedestrian

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Emphasis Area Objectives and Strategies
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C. Reduce motor vehicle speeds C1. Implement traffic calming techniques (P)

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The goals of traffic calming are to reduce motor vehicle speeds, traffic volume, or both.
Reducing motor vehicle speeds has the potential to reduce both the frequency and severity
of bicycle/motor vehicle crashes, and reductions in vehicular volumes ultimately decrease
bicycle exposure to motor vehicle traffic.

Several of the companion guides provide detailed information on traffic calming
techniques intended to reduce motor vehicle speeds. The reader is referred to these guides
for more detailed information on implementing traffic calming techniques. In particular,
the reader is directed to the following objectives and strategies in the respective guides:

• NCHRP Report 500, Volume 10: A Guide for Reducing Collisions Involving Pedestrians

Objective 9.1 C—Reduce Vehicle Speed
▪ Strategy 9.1 C1—Implement road narrowing measures
▪ Strategy 9.1 C2—Install traffic calming—road sections
▪ Strategy 9.1 C3—Install traffic calming—intersections
• NCHRP Report 500, Volume 5: A Guide for Addressing Unsignalized Intersection Collisions

Objective 17.1 H—Reduce operating speeds on specific intersection approaches
▪ Strategy 17.1 H2—Provide traffic calming on intersection approaches through a combination of geometrics and traffic control devices

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