Can local authorities modify statutory speed limits?
State law allows limited changes to statutory speed limits if those changes are based on an engineering and traffic investigation. Q: What is considered in an engineering and traffic investigation? Traffic engineers and police officers examine many traffic and road conditions to determine a reasonable speed limit. Speed studies are performed to determine the 85th percentiles speed, or the speed that 85 out of 100 vehicles travel at or below. This speed is based on the principle that reasonable drivers will consider road conditions when selecting their speed of travel. Other conditions evaluated include number and type of crashes, number of cars, pedestrians, and bicycles, along with physical conditions of the road such as sidewalks, hills, curves, lanes, driveways, intersections, roadway surface, and traffic controls. Generally speaking, a safe and reasonable limit is set at or below the speed at which 85% of the drivers drive. Posting an appropriate speed limit simplifies the job of e
