V85: A Guide To Telraam Speed Measurements

In the statistics offered by Telraam, a certain graph talks about V85. What is that all about?

The V85 speed, or the 85th percentile speed, is the speed that 85% of drivers do not exceed, and 15% of drivers consequently do exceed. This way, V85 speed gives an indication of the typical speeds driven at a specific Telraam location.

Example: If the V85 speed is 45 km/h, for example, that means that 85% of cars drive by your Telraam with a speed of 45 km/h or less.

V85 and speed limits

The V85 speed is not related to the official speed limit in your street. It can be lower, for instance if the speed limit is relatively high and/or if other factors (such as traffic density, the surface quality, or visibility due to large number of bends, etc.) cause traffic to drive slower than the speed posted on the traffic signs. This is often the case on busy roads during rush hour.

Conversely, the V85 speed can also be higher than the official speed limit. This can occur, for example, in some Zone 30 streets where inadequately designed road infrastructure and low traffic volumes allow for higher speeds.

V85 as a general indicator

The V85 speed is - and has historically always been - a widely used indicator in the world of mobility and road safety. The indicator is used to check whether a speed limit is consistent with the road layout and environment. The V85 speed is considered to be representative of the speed that can be safely maintained on a given road.

Value of V85 for citizen scientists and decision-makers

Beyond providing an indication of liveability, the V85 indicator should be put in a broader context. To arrive at policy decisions and interventions, it is important to draw conclusions based on different data (e.g. traffic intensities for different modes, average speed, road characteristics and function) and statistics (e.g. accident figures). Neighborhood residents, experts by experience, are often well placed to identify specific issues. From a participatory approach, such local insights are vital to properly interpret the value of V85.