A portable traffic signal (PTS) system is a traffic control device designed to facilitate the movement of one-way traffic at work zones where there is a temporary lane closure. The 2009 edition of the Manual on Uniform Traffic Control Devices (MUTCD) provides minimal guidance for the use of PTS systems with a pilot car, flaggers, or a pilot car and flaggers. Furthermore, the MUTCD also gives minimal guidance on appropriate signal timings and the traffic volume thresholds for work zones at which a PTS system might fail, and safety could be compromised. Therefore, the objective of this study was to develop a model and provide guidelines for the use of PTS systems in conjunction with pilot car operations by using factors such as the roadway average annual daily traffic (AADT), length of the work zone, length of the green interval, and the pilot car’s round-trip time. Over a 4-week period from August 5, 2014, to August 28, 2014, 161 h of video data were collected at four rural highway work zones in Kansas. The video field data were used to calculate the values for saturation headway and start-up lost time, which were 3.3 s and 6.0 s, respectively. The developed equations and the existing Kansas Department of Transportation policy of a maximum round-trip time for the pilot car of 15 min and a maximum pilot car speed of 40 mph were used to determine that PTS systems would fail to accommodate all traffic at and above AADTs of 7,083 vehicles per day and at a corresponding maximum green time of 446 s. (Author/publisher)
Abstract