Combining Queue Warning with Dynamic Late Merge

In our last post we talked about the ATSSA “Tuesday Topics” webinar held June 27th. Joe Jeffrey began the webinar with a discussion of work zone ITS basics. Chris Brookes of Michigan DOT shared some of his lessons learned. The final speaker that day was Ross Sheckler of iCone there to talk about coming trends in work zone ITS. Ross declared that the next big thing will be queue warning combined with dynamic late merge.

Mr. Sheckler began by looking at the state of our industry. He said that nationally there are nearly 1,000 deployments per year now. Costs of these systems are dramatically lower than they once were. And the economy and simplicity of these systems have not affected their flexibility. In fact, because applications vary, flexibility always has been and always will be an important feature of work zone ITS.

And for that reason it is very easy to add features, including dynamic late merge. As Ross pointed out, queue warning systems have their limitations. When volumes increase and queue lengths extend beyond the limits of a queue warning system additional steps should be taken. By instructing drivers to stay in their lanes and take turns at the merge point, it reduces the overall queue length, makes the best use of limited capacity, reduces road rage, and sometimes can even improve throughout.

In his drawings of typical system configurations he listed 4 sensors and 1 portable changeable message sign (PCMS) for queue warning. For queue warning with dynamic late merge he added a second PCMS at the merge point to tell drivers to take turns and a fifth sensor to narrow the gap between sensors midway through the affected area. So, in total, just 1 more sensor and 1 more sign. This is a minimal added cost and significantly increases the capabilities of the system.

The message here is that we can often solve multiple problems with one system. It just takes a slightly different logic in the controlling software. In this case you can solve problems with end of queue crashes and conflicts at the merge point with one inexpensive, easy to use system. So please remember this the next time you specify a work zone ITS system. Consider all of the challenges you face on that project, and think about ways work zone ITS may mitigate one, two or perhaps even many of them.

This webinar covered a lot of ground in a very short time.  It was recorded and can be viewed by ATSSA members anytime at: Or watch for possible future webinars on this same topic.


Work Zone ITS Lessons Learned

On Tuesday, June 27th the American Traffic Safety Services Association (ATSSA) presented another in a series of “Tuesday Topics” webinars. This one was on Work Zone ITS. These are meant to be short (30 minutes) to fit into everyone’s busy schedules. I spoke first on the basics of work zone ITS. I talked about components, software, and how they were all combined in the field to form different types of systems.

After that introduction Chris Brookes of Michigan DOT discussed some of his lessons learned. He had several interesting points I would like to share with you today. Most of them concerned portable changeable message signs (PCMS). Work zone ITS systems collect data, analyze it, and trigger events but the most important thing these systems do is trigger preprogrammed messages on PCMS. That is the primary way in which these systems affect driver behavior.

His first lesson learned was the importance of using multiple message signs on both the shoulder and median sides of the freeway, especially where you have heavy truck traffic. Shortly after one of his first system deployments, he drove the job to see how it was working and had to call the office because he never saw the message sign. It was on the shoulder next to an on-ramp where trucks were entering the freeway. As a result Chris, and probably everyone else, never saw it. He recommended putting out several signs to be sure the message is seen.

He recommended using portable transverse rumbles trips just before the message signs to wake drivers up so they pay attention to the message on the signs. He said they have found that was especially effective and got far better results than the signs alone did.

Mr. Brookes talked about message construction for queue warning. Message signs well in advance of the slow down should display something like SLOW TRAFFIC / 2 MILES AHEAD. But signs closer to the slow down, especially less than a mile away should not be so specific because queue lengths ebb and flow. For those nearby signs he recommended a message like WATCH FOR BACKUPS.

The one topic that was not focused specifically on message signs was contract language. Chris suggested separate pay items for sensors, message signs, cameras, etc. He said you often get started on a project and find you need additional devices. And by including specific pay items, it makes it fast and easy to add more later on.

There were more questions at the end of this session about his next point than any other. Chris Brookes recommended blanking the message signs when traffic was in free flow conditions. He feels that drivers, especially commuters, who pass the signs regularly will quickly learn to ignore generic messages. But when they pass a sign that is normally blank and now is displaying a message, they will probably pay attention.

This runs contrary to current trends. State DOTs are being pressed by their governors to display something on permanent CMS to demonstrate to drivers that their tax dollars are being used wisely. But it would be a mistake to apply this policy to work zone ITS. These systems are there to reduce crashes in work zones. And we agree with Chris that by displaying messages only when conditions justify it, we will get better results.

This was a short but very effective webinar. It was recorded and can be viewed by ATSSA members anytime at: Or watch for possible future webinars on this same topic.