Portable Rumble Strips: Placement Recommendations for Back-of-Queue Protection and Assessment of Driver Distraction-Reducing Effects

This report documents the results of two research efforts to provide improved guidance on where to place portable rumble strips (PRS) in advance of work zones. The first effort involved a statistical analysis of the probability that the length of queue that forms during a given cycle of alternating one-way operation on a two-lane, two-way roadway does not provide sufficient stopping distance between a) the location of a PRS array deployed at a given distance upstream of the work zone, and b) the upstream end of the queue. If the probability is too high, the value of the PRS array in alerting a distracted driver in time for them to stop before colliding with the queue is diminished. In the second effort, field observational studies of drivers approaching and passing over PRS were performed to determine whether PRS influence the rate of visually-distracted driving that occurs, and whether that influence decreases over time as motorists proceed downstream from the PRS. The results of the statistical analysis yielded tables providing recommended minimum distances of PRS deployments from an alternating one-way operation on a two-lane, two-way roadway. These recommendations varied as a function of the operating speed on the roadway, traffic volumes, and length of the work zone. The results of the field studies showed that nearly one in five motorists are visually distracted in some manner while driving. The studies also showed that this rate of visual distraction decreased at distances closer to the work zone, and observations of distracted drivers as they passed over the PRS indicate that at least some of the decrease in distraction was due to the presence of the PRS. Data were not sufficient to determine conclusively how long the distraction-reducing effects of PRS last. However, data from one site suggest that the effect was limited to the first 1500 feet after traversing the PRS.