85th Percentile Speed – Investigating Modern Use

MetroCount’s traffic analysis software allows traffic managers to quickly and easily identify the 85th percentile speed of a road at the traffic survey site. This statistic plays an important role in identifying speed related issues but can be misquoted if other factors that influence speed aren’t accounted for.


Many Standards (eg AS1742.4) and traffic engineering books define 85th percentile speed as: The speed at or below which 85% of all vehicles are observed to travel under free flowing conditions past a nominated point.

Why Filter 85th Percentile Speed

This video details why traffic engineers use the 85th percentile statistic, where it came from, how it is applied and how it can be easily misrepresented in traffic data.

MetroCount software allows traffic data to be filtered to provide a more accurate 85th percentile statistic and consequently a better representation of the operating speed for road management.

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