Effects of Police Presence on Speed in a Highway Work Zone: Circulating Marked Police Car Experiment

This study evaluated the effects of police presence on the speed of vehicles in a work zone and determined the ‘halo’ effects of police presence (lasting effects when police are gone) on vehicular speeds. A marked police car circulated in a 4-mile long interstate highway work zone and actively enforced the speed limit laws. Variables such as the average speed, speed distribution, percentage of fast-moving motorists, and net speed reductions for cars and trucks were used for evaluation. The results indicated that the average speeds of the cars and trucks were 4.3-4.4, and 4.3-5.0 mph, respectively, lower when police were patrolling the work zone compared to no-police patrol condition. The percentage of fast-moving cars and trucks before the work space decreased by 14% and 32%, respectively, when police were in the work zone. These speed reductions indicate that the police presence was effective in decreasing the speed of vehicles in the work zone. The police presence had halo effects on trucks but not on cars. Trucks traveled at reduced speed when police were present in the work zone and this trend of traveling at the reduced speed continued for a time period at least one hour after the police departed from the work zone. However, cars traveled 2.4-3.0 mph faster and the percentage of fast-moving cars in the work zone increased after the police left the area.