The 85th Percentile
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The 85th percentile is the speed that 85% of drivers do not exceed, and 15% of drivers exceed. Therefore, the 85th percentile speed gives an indication of the typical speeds driven at a specific location. For example, if the 85th percentile is 35 mph, it means that 85% of cars drive at 35 mph or less.
The 85th percentile speed is not related to the actual speed limit. It can be below it if the speed limit is high and other factors such as traffic density, the surface quality, or visibility due to large number of bends, etc. cause the speed of traffic to be generally lower. This is often the case on busy roads during rush hour.
The 85th percentile can also be above the speed limit. For example, in some 30 mph roads where inadequately designed road infrastructure combined with the low traffic volume allow higher speeds.
85th percentile for last 7 days = 33 mph
Measurements to date show that, when installed, the VAS reduces the 85th percentile by 1 mph