Work Zone Performance Measures

I just read an FHWA study entitled, “A Primer on Work Zone Safety and Mobility Performance Measurement” written by Jerry Ullman and Tim Lomax of TTI and Tracy Scriba of FHWA (FHWA Report # FHWA-HOP-11-033). Since SAFETEA-LU we have been wrestling with how best to measure and evaluate work zone performance. Much has already been written, but this report takes the practice to a new level. In less than 50 pages it explains the need for measurement, the types of data that might be used and reasons a state or local agency might choose one or more of them.

I won’t try to create a Readers Digest version of the report here. You will have to read it yourselves and I strongly recommend that you do. But I would like to share a few random thoughts that occurred to me as I read it.


  • They contrasted project level measures with agency/program level measures. Most would agree that work zone ITS systems can help with both. But our focus will always be on the acquisition of project level data.
  • The measures chosen will vary widely from agency to agency for all of the reasons listed in the report. But also because agency goals vary widely. Agencies with urban, congested roads will be more concerned with volumes. Agencies in more rural areas with lower capacity will be focused more often on delays. Also, no two agencies have the same categories or detail of data available to them. Performance measures must be tailored to best reflect the goals of the agency while measuring what needs to be measured.
  • Beginning on page 41 they discuss methods for estimating queues and delays from spot sensor data. What do you system manufactures think about this? Does it agree with your experience? Or would you change something? Please tell us what you think.

Finally, on page 30, they offer some very good advice when using spot speed sensor data:

  • Ensure that sensors will exist within the work zone and upstream for a distance greater than the anticipated length of congestion and queues that may develop.
  • Deploy sensors as closely as is practical and affordable, to increase travel time and delay measurement accuracy.
  • Ensure that traffic sensor spot speed data will be archived for use in work zone performance measure computations.

This fits with my experience. They are three important lessons learned. We often wish we had more data, but I have never been involved with a project where we felt we had too much data. (See “Cameras Versus Sensors, August 27, 2012)

Please read this valuable study and let us know what you think. And, please, pass it on to your fellow practitioners.

Some “Get It” and Some Do Not

ITS California held its’ annual convention and trade show this past week here in Sacramento. More than 200 ITS professionals attended to see the latest products and to sit in on their very timely workshops. Road-Tech was there as well, displaying  automated work zone information systems, dynamic message signs, traffic counters, radar signs and other rural and work zone ITS products.

As visitors stopped at the booth, I was struck by the two distinct types of people we spoke with.  Either they understood work zones or they did not. They either “got” work zone ITS, or they did not.  There is very little gray area in between.

This seems simple enough as I write it here today. But it is something worth considering in more detail. We are competing with the larger ITS world for funding, for projects, and just for attention. ITS professionals understand the tools we use, but often they don’t understand how they should be used or the significant benefits to be gained through their use. To make matters worse, they think they do understand. Everyone drives through work zones so everyone thinks they are experts on work zone traffic control.

This all came to me in an “ah-ha” moment several years ago when I was on the phone with Jon Jackels of Minnesota DOT. I complained that ITS America no longer offered many seminars on work zone or rural ITS at their annual convention. Jon explained that it was because they don’t know anything about work zones. Most in that world come from the technology side: either from the vendors or the agency traffic signal group. Very few of them have ever designed, installed and maintained a work zone.

They understand what their devices and systems can do, but they don’t know what they are trying to accomplish with them. The old saying, “When you are a hammer, everything looks like a nail” certainly applies here.

Those of us who care about work zone ITS need to remember this when we talk with others. We take our training and experience far too lightly. When we are selling the need for systems on a project, we should focus more on the benefits of using the system. Don’t just talk in generalities about increased throughput – put it into hard numbers and back it up with an explanation that people unfamiliar with work zone traffic control will understand. And we should point out that 24% of non-recurring congestion is caused by work zones.  Often the permanent systems are either torn out during construction or missing altogether. Yet that is where these systems will benefit stakeholders the most.

Let’s keep this in mind the next time we discuss work zone systems with others. Consider their level of work zone experience – will they “get it” after hearing the short version? Or do you need to educate them on more than just the systems themselves?