| Some causes of non-recurring road congestion, like work zone activities, weather, traffic crashes, and vehicle disablements are well researched and quantifiable. Police traffic stops occur more frequently than crashes and vehicle disablements combined, though their impact on roadway capacity and operation has not been studied.;Staged stop scenarios using a marked Florida Highway Patrol (FHP) vehicle and civilian research vehicle allowed for researchers to analyze the move over behavior of more than 9,000 outside lane vehicles approaching the police traffic stop. Additional examination Florida Department of Transportation traffic detector data at the location of over 13,000 historical FHP stops, combine to illuminate the subject. The speed of vehicles passing those enforcement stops was reduced in a statistically significant way, 1.3 and 4.6 miles per hour respectively.;Move over laws create a mandate for motorists to vacate the lane adjacent to the stop. Overall, three out of four vehicles move over in compliance with the law. When red and blue lights are used exclusively, compliance is higher, along with earlier merges and greater reductions in speed among non-moving vehicles. Neither opposite direction rubbernecker effect, nor turning off forward-facing emergency lights were found to be statistically significant.;From a highway capacity standpoint, the enforcement stop can be modeled as a theoretical lane blocking event, adjusted for motorists' compliance. Based on this research, police enforcement stops reduce available capacity between 54 and 58 percent on two-lane freeways, 35 and 41 percent on three lane facilities, 23 and 30 percent on four lane facilities, and 14 and 22 percent where five lanes are present. Regression analysis examined factors to explain the speed of vehicles passing stops and showed that the number of lanes, posted speed limit, and ambient lighting conditions were all statistically significant issues.;From a policy standpoint, police should use their emergency lighting equipment throughout the duration of enforcement stops since they improve move over compliance and ostensibly safety. Though not modeled implicitly, breakdown is likely not a deterministic measure, so police activity during periods of high traffic flow and congestion should be reserved for compelling traffic safety needs. |
