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.