How are speed limits primarily determined?

Speed limits are primarily determined using the "85th percentile speed" of free-moving vehicles. This method is based on the principle that when drivers are allowed to travel at a speed they feel safe, the majority of them will drive at a speed that reflects the safe operation of traffic flow on the roadway. Typically, the 85th percentile speed represents the speed at which 85% of drivers are traveling at or below in free-flowing traffic conditions.

This approach helps set a speed limit that is reasonable and representative of how drivers naturally behave on the road, thus contributing to safer driving conditions. It does not rely on extreme cases, such as the fastest recorded speeds (which could lead to excessively high limits) or averages during peak congestion. By focusing on the behavior of the majority of drivers under normal conditions, this method aims to balance safety and efficiency on the roadways.