What is a speed study and why it is sometimes needed?
A speed study is a study of the overall speed along a specific length of road. The study is often needed to find the safe sight/stopping distance for proposed streets or driveways intersecting an existing road. These distances are set as requirements by the county or municipalities. Often times, roads without posted speed limits need a speed study if a reasonable sight distance is not available. Municipalities may conduct a speed study for any number of reasons. Design and physical factors place a limitation on safe operating speeds such as horizontal and vertical curves, hidden driveways and other roadside developments, high driveway density, rural residential or developed areas and lack of striped or improved shoulders. Unless roadway geometry parameters dictate otherwise, speed limits on roadways are set based on spot speed studies and the 85th percentile operating speed. The 85th percentile is the speed at which 85% of the motorists traveling a given road are driving at or below. P
