Evaluation of Portable Traffic Signals in Conjunction with Pilot Car Operations at Two-Lane, Two-Way Temporary Rural Work Zones in Kansas

Abstract

The primary objective of this study was to evaluate the use of Portable Traffic Signal (PTS) systems at long rural two-lane work zones and compare three different conditions for controlling one-lane traffic: flagging only, a PTS system with the presence of a flagger, and a PTS system without the presence of a flagger in conjunction with pilot car operations. The primary measures of effectiveness were determined as Red Light Running (RLR) or noncompliance percentages, vehicle delay estimates, queue lengths, signal timing operations, and general field operations. Data were collected three days per week over a period of four weeks for from August 5, 2014 to August 28, 2014 at four different temporary work zones in Kansas. Two PTS units were used for the purpose of the study in conjunction with pilot car operations. It was found that only nine vehicles were waived through by a flagger to enter the work zone when flagging only operations were in effect. Additionally, when a PTS was used with a flagger, it was found that for 50 vehicles the flagger used discretion and waved those vehicles through the red light and brought a reduction in the total delay. Also, only two RLR vehicles were observed where the drivers simultaneously disregarded the flagger and the PTS unit. Similarly, 92 red light running (RLR) vehicles were observed when a PTS was used without a flagger. A test of proportions conducted on the three samples at 0.05 level of significance indicated that there was a statistically significant difference in the number of violations when a PTS was used with a flagger and when only flagging operations were used. Also, the difference in the number of violations when a PTS was used without a flagger and when only flagging operations were used was statistically significant. Similarly, there was a statistically significant difference in the number of violations when a PTS was used with a flagger and when a PTS was used without a flagger. The results of the test of proportions indicated that there was no statistically significant difference between the number of RLR vehicles that followed an already departed queue for the ‘PTS with a flagger’ and ‘PTS without a flagger’ conditions. Furthermore, it was also found that there was a statistically significant difference between the number of RLR vehicles that left the queue due to the wait time and the number of vehicles that disregarded the PTS control for both the conditions. An exploratory delay analysis was conducted to quantify the amount of total delay reduced by the flaggers when they waved the vehicles through the red light. The analysis indicated that the presence of a flagger reduced the total delay by approximately five percent of the total delay that could have occurred during the normal operations. Additionally, equations were developed to determine the volume thresholds at which the PTS system would fail and the appropriate green intervals needed to serve a certain queue length. It was found that based on the existing KDOT policy of a maximum pilot car roundtrip time of 15 minutes, the PTS system would fail at an AADT of approximately 7,083 vehicles per day and at a corresponding maximum green time of approximately 446 seconds. In conclusion, it was recommended to use a PTS unit without a flagger in conjunction with pilot car operations at long rural two-lane work zones but measures such as engineering studies to more accurately estimate queue lengths, installation of static or dynamic signs indicating the expected wait time, and regular inspections of the PTS units by supervisors or crew members to mitigate excessive delays and monitor for RLR vehicles were suggested.