What percentile is commonly used to establish speed limits according to traffic engineering methods?

The 85th percentile is commonly used to establish speed limits based on traffic engineering methods because it is considered to represent the speed at which the majority of drivers are comfortable traveling on a given road. By setting speed limits around the 85th percentile speed, traffic engineers aim to promote safety while also reflecting realistic driving behaviors. This method takes into account the behavior of the majority of drivers rather than extremes, helping to reduce violations and improve compliance with the speed limit.

Using the 85th percentile also allows for the establishment of a speed limit that aligns with prevailing traffic conditions, rather than an arbitrarily low or high limit that may not reflect actual driving patterns. This practice supports not only the safety of road users but also aids in the flow of traffic by keeping speeds consistent with drivers' expectations.