REDUCING POSTED SPEED LIMITS GOAL

Reducing the posted speed limit will work to potentially slow down motorists’ speeds which will increase safety and decrease crashes.

HOW DOES IT WORK?

Lowering the posted speed limit ideally will encourage people to drive more slowly. This is a low-impact and cost-effective approach; however, reducing the posted speed limit alone likely will not have much effect on the safety of the road for all users. Speeds traveled are based on the driver’s perception of the road and surrounding environment. Therefore, a combination of smart street design and the reduction of speed limits is the best approach and will yield the best results.

Pairing this strategy with others that include road dieting, or the addition of detailing or speed bumps would likely make this a more successful approach. Keeping speed limits within reason is also important. Residential roads, narrow roads, and areas with more development along the sides of streets would be better for a lower posted speed limit. Areas that are more rural and have wider lanes make sense for a higher posted speed limit.

Speed limits are often subject to change based on studies and redefined based on the 85th percentile (speed) that drivers are found driving. This is called “prevailing speed” and is the major consideration for setting speed limits because it is the “safest” speed that 85 percent of drivers are driving. Speed limits should be adjusted based on the majority of what drivers are driving down a corridor or within a defined stretch of road.

Source disclaimer - the article by SEHInc no longer seems to be available but additional information about speed limits is available. A short article with discussion points on the original source article can be found here. One additional source to view about speed limits with similar information can be found here

Although decreasing speed limits might not be the best strategy to implement first, it should be noted that adjusting the speed limit based on other changes should be done after road design and traffic calming techniques are implemented. This is still a useful tactic when trying to discourage slower driving speeds where they do not make sense and prevent significant speeding in areas (highways mainly).