What does legal speed typically refer to?

Legal speed typically refers to the speed limit that is established based on the behavior of the majority of drivers under free-flowing traffic conditions. This is often determined by the 85th percentile speed, which is a common traffic engineering practice. The 85th percentile speed is the speed at or below which 85% of the vehicles are traveling, reflecting the natural driving tendencies of motorists.

Using this measure helps ensure that speed limits are set realistically, improving compliance and safety. When road authorities set speed limits, they may take into account the speeds at which most drivers feel safe and comfortable, which tends to correlate with traffic flow and road design. This approach helps in minimizing accidents and improving the overall efficiency of traffic.

Other options, while they may touch on aspects of speed limits, do not encapsulate the essence of what is meant by legal speed in the context of road design and traffic flow. For instance, speed set by law would include artificial constraints that might not align with driver behavior, while average speed by the fastest vehicles could suggest unsafe conditions if too few drivers are traveling at that speed. Minimum speeds focus more on preventing traffic flow issues rather than establishing a safe traveling speed for the majority.