The Need for Baseline Data

This past week I spoke at an FHWA Peer-To-Peer Exchange on Work Zone ITS. I talked about work zone data: performance measures during and after a work zone is installed, how to collect the data, and lessons learned from past deployments. The DOT folks in attendance were very involved in the discussion and made several rather astute observations. These fell into three groups or themes which I would like to share with you in my next few posts.

The first theme revolved around the need to deploy work zone ITS prior to any other work being done. Work zone ITS systems are used for a variety of reasons but nearly all of them benefit from good baseline data. Most of the meeting participants had used historical data and said it was better than nothing. But that current data would have been more useful.

Historical data are averages. They look at AADT over several months. Those may have been the same months during which construction will take place, but chances are they were not. Furthermore, changes affecting counts are taking place every day. Special events, work on other routes that change traffic flows on your route, weather, economic conditions, and many other changes affect the overall and hour-by-hour counts passing through the work area.

How do you know if the work zone is causing traffic delays if you don’t know what it would be without the work zone? If your system is being used to measure and display delay times, what will you base that on? Delay times are best used on commuter routes. Commuters know better than we often do how long it should take them to get from point A to point B. If we want to be accurate about the delay times we display, we must have an accurate baseline.

There is also the possibility that the algorithm used to calculate delay times results in numbers that are always a little higher or lower than the actual delay times. It is far easier to prove that before a work zone is installed than once the work begins.

If you deployed the system to reduce the number of crashes or incidents, you will also need a baseline. The simplest way of setting that is to deploy your system early and measure the number of times speeds drop below a threshold, say 30 MPH. Then compare that to the numbers once the work zone is in place.

To evaluate a system’s effectiveness, regardless of your deployment goals, you need baseline data. And you don’t have good baseline data if it wasn’t collected just prior to the project start. Everyone who spoke up at the meeting last week had experiences where they wished they had the system in place earlier to collect baseline data.

So as you plan your next project where work zone ITS will be used to mitigate traffic impacts, be sure to bring the system in a few weeks early. It gives the contractor time to iron out any issues and, more important, it will provide you with the very latest counts, speeds, volumes, or whatever you choose to measure. By comparing current baseline data with the data after the work zone is in place, you will make better decisions about work zone design, work windows, and much more.

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