Space headway and safety of platooning highway traffic

This study examined spacing characteristics and safety of platooning vehicles on highways. Even at low volume conditions platooning occurred. When time headway was 4 seconds or less the vehicle was considered in platoon. The percentages of platooning vehicles were 61% and 76% when hourly volumes were 269 and 502, respectively. As the volume increased the percentage of platooning and platoon size increased too. At 269 vph, 60% of platoons were two-vehicle, but it decreased to 47% when the traffic volume was 502 vph. The percentage of larger platoons increased with volume increase. The field space gaps were calculated and compared with car following distances. Over half of the vehicles kept space gaps that can be traveled in 1.5 seconds or less. Such short distances may not be enough for safe driving, when there lead vehicle makes sudden deceleration. Platooning characteristics are important in selecting automatic cruise control and longitudinal control in ITS. The findings from this study indicated that the platooning vehicles on highways did not have the minimum stopping sight distance recommended by AASHTO(1).