Speed Limit Investigations

The Winston-Salem Department of Transportation (WSDOT) frequently receives questions about speed limits and requests for changes in speed limits. Speed limits are intended to designate a "safe speed."  Speed limit changes are most effective when accompanied by changes in roadway characteristics, such as sight distance and lane width.

  • North Carolina General Statute 20-141 sets all speed limits within municipal corporate limits at 35 mph unless the City Council establishes another limit. The statute requires a traffic engineering investigation before speed limit changes are considered.
  • Speed limits established by City Council can range from 20 to 55 miles per hour in five-mile per hour increments.

Requesting a speed limit or traffic engineering change

Listed below are the procedures that the WSDOT uses for speed limit, stop sign, or other traffic engineering changes:

  • A citizen requests a change.  Requests can be made by phone, mail, or e-mail.  Written requests or petitions are not required.
  • WSDOT conducts an investigation to evaluate the concern and to assist in developing a recommended solution. These investigations may include:
    • a field investigation of the site;
    • hourly or daily traffic counts;
    • speed studies taken during various times of the day (see information on the 85th percentile speed, below);
    • studies of the delay experienced by vehicles due to roadway conditions;
    • accident history investigations.
  • WSDOT compiles the data and develops a recommended course of action. Some examples could be:
    • a request that the City Council approve a speed limit change.  Please note that speed limit signs are effective only in treating speeding by drivers who are unfamiliar with the roadway, they are not effective in dealing with residents who speed.
    • installation of a center line on the roadway.  This has been shown to be very effective in reducing speeds on some types of roadways.
    • installation of an edge line on the roadway.  This may be effective in reducing speeds on some types of roadways, especially when combined with roadway center lining.
    • a change in on-street parking.  This can help address sight-distance concerns.
    • installation of advance warning signs.  This alerts the driver to unexpected conditions and, in some cases, reduces speeds and accidents.
  • If WSDOT recommends a speed limit change, a Council Action Request Form is submitted.  Under State law, the above mentioned studies are required before speed limit changes can be recommended. Once the request is approved by the City Council, WSDOT installs speed limit signs. 
  • If WSDOT recommends a center or edge line in a residential neighborhood, the residents are contacted for approval of this recommendation prior to a permanent installation.  
  • If WSDOT recommends a STOP sign installation, it can be installed without City Council approval. STOP signs are ineffective for speed control and will not be used for this purpose.
  • The 85th Percentile: Spot speed studies collect free flowing vehicle speeds using a radar or a laser gun. A sample of 100 speed measurements provides a statistically valid database and yields a valuable statistic, the 85th percentile speed, that is the speed at or below which 85 percent of all traffic is traveling. This determines the point where a speed limit should be set. National studies show that the 85th percentile speed reflects the driving public's perception of a safe and reasonable speed. Statistically, speeds above the 85th percentile are not considered to be a reflection of reasonable driver behavior. The primary purpose of speed limit signs is to inform the unfamiliar or unsure driver of the maximum safe speed for the road under normal conditions.  Posting speed limits that are artificially low or high for the road conditions have little effect on most driver speeds.   

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