4.5.3 Percent of Free-Flow Speed (PFFS)

Free-flow speed is defined as “the average speed of vehicles on a given segment, measured under low-volume conditions, when drivers are free to drive at their desired speed and are not constrained by the presence of other vehicles or downstream traffic control devices.” PFF) is expressed as a percentage. Per the HCM, PFFS is defined as “the average travel speed (ATS) divided by the free-flow speed.”