SPEED LIMITS PURPOSE

Traffic operates the safest when vehicles in the traffic flow are traveling at a uniform speed. Posted speed limits can help keep the traffic flowing smoothly if most drivers find the posted speed limit comfortable and reasonable. This is called “voluntary compliance”. To best achieve voluntary compliance, speed limits must be consistent throughout the state. When established properly, posted speed limits are essential for law enforcement to identify excessive speeds and curb unreasonable behavior.

Speed Limits: Why Do We Have Them?

SPEED AND SAFETY

Research shows that posting a lower speed limit has very little effect on changing speed patterns if the roadway remains unchanged. Drivers are much more influenced by changes to the roadway’s geometry, its environment and surface or traffic conditions. Lower speed limits can reduce crash severity, however they do not necessarily reduce crash frequency. In fact, posting a lower speed limit than the flow of traffic can actually increase the risk of crashes because it creates a greater speed variance between the slowest and fastest-moving vehicles.

HOW SPEED LIMITS ARE SET

Minn. Statute 169.14 establishes statutory speed limits on most typical roadways under ideal conditions. Unless otherwise posted:

• 10 mph in alleys
• 30 mph on streets in urban districts
• 55 mph on other roads
• 65 mph on expressways
• 65 mph on urban interstate highways
• 70 mph on rural interstate highways

SPEED LIMIT GUIDANCE FOR MUNICIPAL ROADWAYS

The Minnesota Local Road Research Board (LRRB) recently released a study on local speed limits. This guide examines the history of speed limits, the recent statutory change and consequences to communities. It also examines the effectiveness of speed limit changes and outlines a process to follow when deciding to make a change.

CHANGING THE SPEED LIMIT

To change to the speed limit, the County must formally request a speed study to be completed by MnDOT. During the study, vehicle speeds are collected during a set time period. The new “appropriate” posted speed is determined by identifying the 85^th-percentile speed, meaning the speed at which 85 percent of the drivers are travelling at or less. This 85^th-percentile is a national standard that is used to represent uniform traffic flow described above. If the 85^th-percentile speed is found to be higher than the current posted speed limit, the speed limit may be increased. If the 85^th-percentile speed is lower than the current posted speed limit, it is possible the speed limit may be lowered. Other factors such as traffic operations and crash history are taken into consideration as well.

MORE INFORMATION

Carver County Speed Limit Handout 

Please visit MnDOT’s website for further information.