Perception-Response Time (PRT) is important to analyze a driver’s response to a collision. PRT consists of reaction time, limb movement time (foot, hands), and a vehicle latency time. PRT requires the perception of an immediate hazard that requires an emergency response.
It must be noted that PRT does not include the detection time. An object must be detectable, in order for a driver to respond to it. If a driver cannot detect an object (e.g. very dark object at night), then the driver cannot respond to it.
PRT can be different, depending on the type of scenario involved. For example, a driver would be expected to respond quickly to a yellow traffic light. Also, a relatively quick response would also be expected for an identifiable pedestrian stepping off the curb into a crosswalk. However, a driver may respond slower as she/he closes on a stopped tractor-trailer, in her/his lane, on a straight highway.