Evaluation of Speed Limits in Kentucky

The objectives of this study were to examine current criteria and procedures used for setting speed limits on public roads and to recommend appropriate speed limits for various types of roadways. The major components of the study were a review of the literature, the collection and analysis of speed data, and the collection and analysis of accident data. The speed data showed that operating speeds for most types of highways are substantially above the posted speed limit and that speeds of cars are slightly above those of trucks. Data taken before and after speed limit changes show that operating speeds are changed much less than the change in speed limit. Speed data taken in construction zones show that, while speeds are lower than typical for the specific type of highway, there is a disregard for lowered speed limits. A comparison of accident rates at adjacent sections of interstate showed no increase in either total, injury, or fatal injury rates at locations with a 65 mph (104.6 kph) speed limit compared to a 55 mph (88.5 kph) speed limit. Except where legislatively mandated speed limits apply, the 85th percentile speed should be used to establish speed limits. Maximum limits are given for various types of roadways. In many instances, the maximum speed limit is slightly higher than the existing limit. Also, different speed limits for cars and trucks are recommended for some roadways. An engineering study must be conducted before the speed limit is increased for any specific section of roadway.