An Evaluation Framework for Work Zone ITS

Several interesting papers were presented at TRB this past January. Those were recently made available on the web. We will review and comment on a few of them here beginning with 14-1022: “Effectiveness of Work Zone Intelligent Transportation – Evaluation Framework and Case Studies” by Praveen Edara, Andrew Robertson and Carlos Sun.

They suggest that we need a standard method of evaluating work zone ITS. While I agree with their conclusions, I don’t feel they offer any new ideas in this paper and they don’t go far enough. Their methods are already the recognized approach: measure the effectiveness of the system and compare it to the costs to find a benefit/cost ratio. And the numbers they arrive at are not a full measure of the worth of a system.

Specifically, they suggest we should focus on five measures of work zone ITS effectiveness:

  1. Diversion.
  2. Delay Time (or Travel Time).
  3. Queue Length.
  4. Crash Frequency or Crash Rate.
  5. Speed Based Measures, including 85th percentile, speed compliance or speed variance.

The measure or measures chosen will vary with the goals of each project. By the way, in their review of existing literature, they found that far more papers evaluated work zone ITS results from a traffic operations perspective than from a safety perspective. I think this is a reflection of the reality we have all encountered: everyone claims safety is most important, but actions and dollars normally flow to efficiency.

Anyway, they then chose a measure and after assigning standard values to it, they did the math and found a savings in traveler delay or a reduction in crashes. This was then compared to the cost of the system. What’s new about any of that? It is a good primer on the process, but one with which we are already very familiar.

Here they made a point I disagreed with. They said that when work zone ITS is evaluated on low volume roads, the results are often inconclusive. That makes good sense if you are looking at it from a traffic operations perspective. If you don’t have traffic volumes, there won’t be any efficiencies to be found. But it is not true for safety. Queue warning on long lonesome roads with poor sight distances can be a very effective use of work zone ITS. The systems are inexpensive and one serious injury avoided will pay for it many times over.

They go on to suggest that the benefits of using work zone ITS will be far more apparent on high volume roads, especially those at or near capacity. When we are doing formal system evaluations we should certainly keep that in mind.

But they should have gone a little further. The success of the deployment must be a measure of the degree to which it met the original goals. If those goals were related to reducing delays, then that must be the test. But once you begin to calculate the value of that system, you must go beyond those goals to find the true benefit/cost ratio. Yes, the system saved travelers some time. Quantify that. But it also prevented a few crashes. It may even have saved a life. Those safety improvements should be included in the final calculations or this Evaluation Framework is incomplete.  If we are going to standardize our approach, let’s do so in a way that captures the true value of these systems.

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