By: Philip Garvey
Often the only clue that drivers are approaching an exit in a work zone is a larger gap in a continuous stream of standard orange-and-white-striped panels or drums. These gaps are hard for drivers to detect at reasonable distances.
Drivers have trouble finding freeway and arterial exits when they’re in the middle of a construction work zone. Often the only clue that drivers are approaching an exit is a larger separation, or gap, in a continuous stream of standard orange-and-white-striped panels or drums.
These gaps are hard for drivers to detect at reasonable distances, and they are difficult to distinguish from similar breaks that occur due to faulty device placement and devices being knocked over by wind or passing cars and trucks. This difficulty in finding the exit can result in erratic last-minute braking and turning, driver confusion and anxiety, and dangerous excursions into the work zone. It has recently been suggested that placing differently colored drums and panels in the exit area might improve exit safety under these conditions. In 2005, this low-cost safety strategy was tested on Pennsylvania roadways with promising results. Additional research being conducted at the Thomas D. Larson Pennsylvania Transportation Institute (LTI) at Penn State is further developing this idea through an extensive research project to evaluate green-and-yellow devices. At the end of 2007, LTI completed the first phase of this research: a test track study for PennDOT where the devices underwent controlled field evaluation.
Beating the standard
A full-scale replication of a common right-lane-closure work zone that passed through a right-hand exit was installed. Six channelizing scenarios were tested, three with standard orange-and-white drums or vertical panels marking the exits and three with the experimental green-and-yellow devices. The drums and panels were spaced 40 ft apart on the tangent sections of the work zone and 20 ft apart in the tapered exit area. When green-and-yellow exit channelization devices were used, they were extended five devices (for a total of 160 ft) upstream into the approaching tangent section of the work zone.
A group of 80 older and younger, male and female Pennsylvania drivers participated in the research. Forty subjects drove through the work zones at night and 40 under daylight conditions. Each subject was tested individually. The subjects were seated in the driver’s seat of the experimental vehicle and instructed to drive around a curve in the track at 25 mph toward the work zone and to accelerate to 35 mph once they entered the tangent section and to continue at that speed through the work zone. They were told that they would do this eight times and that sometimes they would need to take a right-hand exit somewhere within the work zone. They were instructed to exit the travel lane when they felt it was safe and appropriate to do so.
Mixed within the six channelizing-device scenarios (that included an exit) were two scenarios where the exit was blocked. These “catch trials” ensured that the subjects were honest in reporting exit detection. Once they exited, the subjects were directed to drive back to the starting point at the other side of the track. A data-collection crew then changed the work-zone-channelizing-device scenario and the next scenario was evaluated. This was repeated until the subject drove through all six candidate scenarios and two catch trials.
Analysis of the data revealed that the green drums and panels made the exits detectable significantly farther away. On average the experimental devices outperformed the standard devices by about 50 ft, or 35%.
When asked if they noticed anything unusual about the devices, 99% of the subjects responded that some of the devices used different colors. When asked if they knew what the green-and-yellow devices were for, 83% said they were there to mark the exit. Finally, when asked if the new devices helped them find the exit, 98% of the subjects said yes.
Based on these promising results, LTI is planning a full-scale field implementation and evaluation of these devices throughout the 2008 construction season, where multiple freeway and arterial construction sites across PennDOT’s 11 engineering districts will be outfitted with these experimental channelizing devices.
About The Author: Garvey is a senior research associate with the Pennsylvania Transportation Institute, Penn State University.
