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Speed Limits

Contact your local District Traffic Operations office.

How are speed limits set?

Speed limits on state roads are based on the results of thorough engineering and traffic investigations.

Factors considered include:

  • Roadway characteristics and shoulder conditions, such as curves, striping and surface width and type; grade alignment and visibility.
  • Roadside development factors, such as sites along the location which generate traffic.
  • Safe speed for curves or hazardous locations
  • Parking practices and pedestrian activity
  • Traffic volume
  • Crash history
  • Traffic signals
  • Speed study

The speed study is the most important part of the traffic investigation. When choosing a speed, drivers take many roadway environmental factors into consideration. Therefore, the speed that the majority of people consider appropriate is an important piece of information. This data is collected by performing radar checks at selected locations on the roadway under ideal driving conditions. An analysis is then conducted on the results to determine the 85th percentile. This is a good indication of the speed under which most (85%) drivers are traveling. Experience has shown that posted speed limits near this value are the maximum safe and reasonable speed. Studies have shown that traveling much faster or slower than this value can increase your chance of being in a crash.

What are the state's statutory speed limits?

Statutory limits are based on the concept that most motorists can operate safely at certain preset maximum speeds under ideal conditions. Whether the speed limit is posted or unposted, drivers are required to reduce speeds below the posted limit for poor weather conditions, curves, hills and potential hazards such as pedestrians. Drivers must also reduce speed when approaching emergency vehicles with emergency lights flashing.

The most common statutory speeds are:

  • 70 mph on interstate highways
  • 65 mph on multi-lane divided highways
  • 55 mph on other roads

Whenever these statutory speed limits are inappropriate for a specific highway, DOTD may establish a reasonable and safe, lower maximum speed limit.

What do the different types of speed limit signage mean?

Regulatory Speed Limit Sign

The black and white regulatory speed limit sign shows the maximum speed that a motorist may travel under ideal conditions.

Advisory Speed Sign

The black and yellow advisory speed sign is used to advise motorists of a comfortable speed to navigate certain situations. It is used with a warning sign. For instance, when traveling on a winding road, the curve warning sign would be used with an advisory speed sign.

Speed limits in School Zones

The department may establish school speed limits on state highways, within a school zone, on the basis of an engineering and traffic investigation. This regulatory speed limit is in effect for specified times or when supplemental yellow lights are flashing.

Speed limits in Work Zones

Temporary speed limits in construction zones are sometimes needed for long-term construction projects or detour routes. These black and white signs are used when a reduced speed is needed for driver and worker safety and are valid 24 hours a day, 7 days a week.


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