Common Mistakes in Work Zone ITS Lessons Learned During 20 Years in This Field

Today, we would like to discuss common mistakes agencies make when including work zone ITS in a project. But we don’t want to scare anyone away or make this more difficult than it really is. Today, work zone ITS is easy to use, easy to contract, and easy to evaluate. So please dive in and learn your own lessons as you go along.

But with that said, there are a few bits of advice we can offer from our many years deploying these systems.

The first is simple enough. Before you specify a system in a project, identify and clearly state your agency’s goal for that system. Is it end-of-queue crash reduction? Is it diverting traffic onto alternate routes? Is it speed reduction? You and every other decision maker in your agency need to agree on the primary goal, and then communicate that goal to the system supplier through your specifications.

Second, don’t try to do too much with your system. Focus on that primary goal first. If the system supplied can also handle additional responsibilities, then add those that help you meet any secondary goals. For example, a queue detection system can also provide traffic data to meet the Federal Work Zone Safety & Mobility rule. But don’t add features that will just bombard you with data you can’t use. You will have plenty to work with as it is.

Once you have your goal for the project, you can begin designing your system. If the goal is reducing rear-end crashes in slow and stopped traffic, doplar radar is the best sensor to use. It works well at low speeds and is inexpensive. But if your goal is to replace a permanent system that measures speeds, counts and classifications, a side-fire radar such as Wavetronix or RTMS.

Next choose your sensor locations. For most systems you will space them about three-quarters of a mile apart. You may get away with as much as a mile or more in some situations, but more often you will want them between a half-mile and a mile apart. Once they are in place and collecting data, check that data to be sure it is what you need. Locations with a lot of concrete barrier sometimes result in radar echo giving you false results. Locations such as a gore point at the on-ramp from a truck scales will result in below-average speeds as trucks slowly speed up onto the mainline.

Budgets often force you to limit the scope of your system. If it comes down to a choice between cameras or more sensors, please consider maximizing the number of sensors. Better, richer data will result in a more responsive system, and one less susceptible to service interruptions. If you must have cameras, limit their use and the video frame-rate to keep your wireless expenses lower.

Your specifications should include the type and quantity of sensors, message signs, camera trailers and other devices. And consider including a line item for each type of device. In that way, you will have a price if you find you need to increase or decrease the quantity of devices.

Finally, dig into your data. Learn what makes the system work. When an incident happens, look at the data to learn how quickly it affected traffic upstream. And how quickly it clears once the cause has been corrected. This will give you a better sense of the capabilities of these systems and how best to use them on future projects.

Mitigating Work Zone Safety and Mobility Challenges Through ITS – Part 2

In our last post we reviewed “Mitigating Work Zone Safety and Mobility Challenges Through ITS” (Report # FHWA-HOP-14-007) and looked at the use of “commercial off-the-shelf” systems to mitigate work zone traffic impacts. Queue systems are the most common example. But these systems also include travel time, dynamic merge and trucks entering/exiting systems.

This report also compared these with the use of custom systems and the use of permanent ITS either alone or supplemented with portable devices. As work zone ITS becomes more “plug & play” this will become much easier to do. And as it becomes easier, it also becomes the more cost effective option.

First, let’s consider off-the-shelf versus custom systems. A few short years ago all systems were, in effect, custom systems. But as time went on, common applications emerged. Dynamic merge was probably the first off-the-shelf system. This morphed into a queue warning system a short time later. Clearly, if a standard system does what you need it to do, there is no reason to consider custom systems.

But when you need something a little different, a custom system is still a good option. This study uses as an example a work zone delay performance measurement system. They used a variety of sensors to measure performance in real time and to provide that information to the DOT and the contractor.

The cost of a custom system is based on the complexity of the system, the time needed to integrate non-standard devices, and the follow up testing. They can be expensive but often these changes can be made quickly and easily. It just depends on what you are trying to accomplish. There are at least two things to consider: 1) once you have a concept of operations, try to get multiple proposals. Every system has underlying design features that help or hinder adaptation to your special application. You will find that one is probably much better suited than the others. 2) Focus your efforts and the system design on your primary goals for the project. Don’t try to do too much. Costs increase sharply with complexity while the likelihood of success falls.

Permanent ITS can sometimes give you all you need to monitor and mitigate work zone impacts. Cameras, sensors and dynamic message signs are often located in and around work zones, especially in urban areas. But two conditions must be met for them to be used for a work zone: 1) They must remain operational throughout the project. Sensors, in particular, can be a problem, and 2) they must be located at advantageous locations. A message board in the middle of the job isn’t much use in warning drivers about delays.

The use of permanent systems also depends on the goals of the deployment. If your goal is to reduce end of queue crashes, you will need sensors spaced close together. Most portable systems space sensors no more than a mile apart and often as little as a half mile apart to recognize queuing quickly and warn drivers upstream. There are locations with that number of side fire radar sensors, but they are rare.

The sensor network used for work zone impact mitigation must also fit the work zone. Much has been written recently about the use of cell phone travel time data but, at least for now, that data looks at road segments that only occasionally match up with work zones. You can monitor travel time through a corridor, but you won’t know where in that corridor (and work zone) a problem has developed.

This does not make these permanent devices useless. As this study points out, combinations of permanent and temporary devices can be used in combination to meet your requirements. It’s simply a matter of understanding the advantages and disadvantages of each.

Mitigating Work Zone Safety and Mobility Challenges Through ITS

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.