United States Department of Transportation
i
operations at two-way long temporary work zones.
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2016-05-01
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[PDF-3.98 MB]
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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 to compare three different conditions for controlling one-lane traffic in conjunction with pilot car
operations: flagging only, a PTS system with the presence of a flagger, and a PTS system without the presence of a flagger.
The primary measures of effectiveness were determined as Red Light Running (RLR) violation 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 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 the percentage of violations for the flagger only, PTS with a flagger, and PTS without a flagger
were 1.1, 1.3, and 3.1 percent, respectively. A test of proportions conducted on the three samples at a 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 without a flagger, as compared to when flagging only operations were used. 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. It was also found 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. It was found that
there was a statistically significant difference in the number of RLR vehicles that left the stopped queue and the number of
vehicles that disregarded the PTS control for both the conditions.
An exploratory delay analysis indicated that the presence of a flagger reduced the total delay by approximately 5
percent of the delay that could have occurred during the normal operations when flaggers waved the vehicles through the red
light. Finally, 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 annual average daily traffic (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 other measures were suggested, such as engineering studies to more accurately estimate
queue lengths, installation of static signs indicating the expected wait time, and regular inspections of the PTS units by site
supervisors or crew members to mitigate excessive delays and monitor for RLR vehicles.
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