Free flow speed

Free flow speed is a reference speed generated by Traffic Analytics, representing the speed at which traffic flows on a road segment when it is not slowed by congestion. This field is useful if you don’t have a reference speed and want to generate an approximate congestion factor from the Traffic Analytics dataset. The field is in kph, expressed to one decimal place. As with the LENGTH field, it saves on file size to look this up in a separate lookaside table, rather than requesting it in your dataset, since otherwise it repeats the same speed for every epoch in a specified road segment.

This field is currently calculated from the 80th percentile of weekend overnight probe speeds over a few years, if there is a minimum amount of probe data. If there isn't sufficient historical probe data to determine an overnight speed, then it's set based on map attributes like speed limit and speed category. Additional rules govern some special cases based on road types. If you are basing critical analysis on a traffic free flow speed, HERE encourages you to use an alternate source of the free flow speed, whose calculation you can design to meet your exact needs.