We love studies in this business. And we have been conducting them on the subject of work zone ITS for some time now. But FHWA published another last January that deserves mention. “Mitigating Work Zone Safety and Mobility Challenges Through Intelligent Transportation Systems” (Report # FHWA-HOP-14-007) touches on several areas I would like to mention here.
This report was written by Jerry Ullman of TTI and Jeremy Schroeder of Battelle. They include several different case studies and draw lessons from each one. But first they talk about work zone ITS in general and point out that, “work zone ITS is now evolving from being an developmental strategy for improving safety, operations, and productivity to more of a “mainstream” tool available to the work zone planner/designer and developers of transportation management plans (TMPs) to mitigate specific safety and mobility challenges that can exist on a project.” Many states still treat this technology as something new and unproven, so we are gratified to see this stated so unequivocally.
The first section looks at an off the shelf queue warning system used in two locations in Illinois. The results are startling. “A preliminary analysis of the I-70/I-57 project crash statistics from 2010 (prior to system implementation) and 2011 (after system implementation) saw nearly a 14 percent decrease in queuing crashes, and an 11 percent reduction in injury crashes, despite a 52 percent increase in the number of days when temporary lane closures were implemented in the project.” This is why any project where capacity issues or geometry will likely result in unexpected queuing, should use some form of queue warning system.
One of these projects included 20 portable cameras, while the other did not. The researchers wrote that, “Camera coverage is useful, but not necessarily essential, for a successful system – At the I-70/I-57 project, traffic cameras were not specified by IDOT but were included in the final system deployed. Both IDOT and the contractor subsequently commented that the cameras were valuable for identifying and verifying when and where traffic issues arose and quickly determining how to best respond to mitigate the issues. However, the lack of cameras on the I-57/I-64 project was never mentioned as a problem by project staff. This could be due in part to the different project lengths involved. The I-70/I-57 work zone ITS covered significantly more interstate mileage than did the I-57/I-64 project. In addition, the loss of shoulders, reduced lane widths, etc. throughout the I-70/I-57 project meant that a stall or crash anywhere within the system coverage limits was fairly likely to cause a traffic queue. Conversely, the bottleneck location at the I-57/I-64 project was constrained to right at the interchange itself, a much more concentrated location that could be reasonably inspected other ways. Consequently, camera coverage to view reasons for traffic queues that developed was considered important at the one project, but less so at the other.”
Finally, the study had some good advice on estimating delay times. “Calibrate to slightly overestimate delays – Project personnel at the I-57/I-64 project noted that they found (primarily through anecdotal conversations with friends and neighbors) that it was more acceptable to the public to slightly overestimate delays when disseminating this information, but not acceptable to underestimate delays. Consequently, calibration of the systems relative to the delays calculated and presented on the signs should ensure that the delays being presented, if in error slightly, err towards the side of overestimation.”
This study offers solid, common sense advice to anyone involved in deploying work zone ITS. We will talk more about it in our next post.