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Flagger Effects in Reducing the Likelihood of Rear-End Collisions for In-Platoon Vehicles in Work Zones

Rear-end collisions are among the most dominant crash types in work zones. Three factors may increase the potential of rear-end collisions in work zones: following too closely, speeding, and faster trailing. This study explores the effectiveness of flaggers in reducing the frequency of these three factors. Eleven data sets were collected from five single-lane work zones with no lane change opportunity. Time gap and speed data for around 4,600 in-platoon vehicles were used. Statistical analyses were based on the frequency of the three factors. According to the results, during flagger presence and a 45 mph speed limit, the probability that a vehicle in platoon would follow too closely was reduced by 60% to 69% compared with a 45 mph or 55 mph speed limit and no flagger. The probability that a vehicle would speed by at least 5 mph at short time gaps was reduced by 28% to 72% during flagger presence and a 45 mph speed limit compared with a 55 mph speed limit and no flagger and by 85% to 95% during flagger presence and a 45 mph speed limit compared with a 45 mph speed limit and no flagger. Work zones with a 45 mph speed limit and no flagger were also found to be more hazardous for speeding at short time gaps than work zones with a 55 mph speed limit and no flagger. Only two of the vehicles were found to faster trail at short time gaps. Because of the low frequency, no statistical analysis was conducted for faster-trailing vehicles.