RESEARCH
Path Intrusion Response Times and PRT Charts
Definition of Terms:
We cannot apply a perception-response time (or use the chart above) until an object is easily identified as an immediate hazard (Conspicuous).
Objects: A "stimulus" or object as defined in this research is something the driver was responding to. Therefore, if there are 5 other cars, 2 birds, 4 pedestrians and one of them come into the driver's path, then that would be a response analysis for a response to one stimulus. A multiple stimulus event is if the driver was responding to one object and within 0.1 to 1.5 second later, he or she was expected to respond to a second object. The first object could be a car, dialing a cell phone, or anything else that required a response. If a driver is already engaged in one response, his or her response to a second object will be delayed by approximately 0.5 seconds when responding to a lead vehicle and approximately 0.7 seconds when responding to a path intrusion.
Straight versus Curve/Cue/Intersection: Straight means there were no significant changes in elevation in the immediate area. You could have a straight upward grade, flat grade or downward grade (less likely). Otherwise, select Curve/Cue/Intersection if responding (or expected to respond) after the knoll of a hill, entering or within a curve in the road or entering or within an intersection.
Day or Night: Select Day if before sunset, night if after sunset and if dusk, look at the range between column for "Day" and "Night".

Eccentricity: The number of degrees from straight ahead from the subject driver to the closest portion of the intruder or intruding vehicle when that intruder crossed the stop line or analogous location. As an example, if a pedestrian emerged from behind a roadside vehicle and was 5 degrees to the driver’s right at the time, the eccentricity would be assumed to be near 5 degrees unless there is direct evidence stating where the driver was looking.
From a Stop: If the Subject driver (responder?) never saw the intruder stopped, then use the lower portion of the chart.
Lanes: Number of lanes from which the intruder emerged from in a continuous motion.
For example, if a vehicle cut from the left lane all the way to the right lane on a highway with three lanes, enter "Multiple Lanes". If that same vehicle moved first to the center lane, then swerved from the center lane into the right lane (in a stair-step movement), use "One Lane".
This chart estimates the average response time for each scenario within 0.43 seconds. If a study reports a number significantly different than that listed above, compare the methodology of the study with that of your case. If the methodology of the study is different, response times could change significantly. For instance, Rice et al (1972) and Lerner et al. and Winter essentially conducted the same study. Each author rolled barrels into the path of a driver, yet Rice, et al. reported an average response time of 0.64 seconds, Lerner at al reported an average response time of 1.51 seconds, and Winter reported an average response time of 1.74 seconds. The differences can be directly associated with the differences in the methodologies. Rice et al. measured response time up to throttle release, Lerner et al. measured response time up to brake application, and Winter measured response time up to full braking of a truck with air brakes. If we account for the methodology differences, these three author’s findings dovetail nicely in that leg movement time is near 0.5 seconds (Muttart, 2004), and braking time takes near 0.25 to 0.3 seconds (Muttart, 2005, Ising et al., 2012).
This chart offers average response times of drivers based upon the variables listed. Obtaining the original research is always recommended and/or an analyst may purchase Interactive Driver Response Research [I.DRR]. I.DRR is an Excel ™-based reference tool, like a digital book, that also allows the user to analyze a driver’s response by accounting for several more variables, as well as utilizing the results from numerous studies.
It is extremely important to understand that these are PERCEPTION-RESPONSE times. Therefore, apply these numbers only after a point when the object should be easily perceived as an immediate hazard (conspicuous). Not only do these times assume perception, they also include vehicle response. These are not "reaction" times; a reaction is the first movement in response to a stimulus (as with taking your foot off the throttle). These numbers represent a time period from perception until first VEHICLE response (the very first lateral movement in a steer or the start of a skid mark [or sharp deceleration] for a braking response).