Portable Traffic Signals as Work Zone ITS?

20160623_065843Today there are many definitions of work zone ITS. I’ve always felt that just because a device is controlled by electronics and some amount of internal software, does not qualify it as work zone ITS. Good examples are portable changeable message signs or portable traffic signals. In their simplest form they work independently and do not react to their environment.

But recently we started a project with portable signals that should qualify. Before the job bid we suggested portable signals as a cost-effective alternative to hardwired temporary signals mounted on posts and powered by a generator. The agency agreed but asked for most of the optional features mentioned on Horizon’s website. Those included wait time display, drive way assistance device, emergency vehicle preemption, and remote monitoring and notification.

Let’s look at each of these in a little more detail.

The wait time display is a changeable message sign attached to the articulating arm of the signals. When the signal at the other end of the work zone is green, the one facing stopped traffic tells it the maximum time they can expect to wait. Then, once the signal on the other end goes to red, it displays a countdown to green equal to the remaining clearing time.

This is a great feature when the work zone is especially long or when drivers on one end of the work zone cannot see the other end. Like travel time systems, once drivers know what the wait time is, they don’t seem to mind it as much. But not knowing often upsets them.

20160623_065949The driveway assistance device is another clever addition. The display consists of a red light and two flashing red arrows, one pointing right and the other left. When the light is red, drivers are expected to stay put. But when the right arrow is flashing, they can turn right when it is clear. The device ties into the signal phases on the main line. The system knows when traffic is moving to the right and tells the driveway assistance device to inform any drivers there that they may do so, too. It’s similar to a WAIT FOR PILOT CAR sign, but starts the moment traffic is cleared to go in that direction.

Emergency vehicle preemption is the same as most permanent signals use. It immediately turns the signal on the other end red, but still must give the same clearance time before turning to green for the ambulance or fire truck. Because these signals are farther apart, sometimes a half mile or more, the emergency responder must still sit there until traffic clears. Otherwise the potential for conflicts exists. This is one feature I would not recommend again, except when the signals are set up for a conventional intersection where clearing time is minimal. Or when there is an especially high volume of traffic that would otherwise extend the green time without preemption.

Remote monitoring is just what it sounds like. The signals report to a server over a wireless digital modem. All aspects of signal operation are monitored. If a lamp fails, or power drops, or communications between signals are lost; an alarm is sent to everyone concerned via text or email. Signal operations are also logged with each phase date & time stamped. So if a motorist claims they were green when they were actually red, the agency would be able to prove that.

Traffic engineers have taught drivers to expect traffic signals to do certain things. Portable signals can now do anything that permanent ones can do. That reinforces those lessons and makes our work zones safer.

Jump Start Work Zone Intelligent Transportation Systems in Your State

screenshot-expo atssa com 2016-02-08 10-56-28

We just got back from ATSSA’s annual Traffic Expo held this year in New Orleans. The focus of this show, more than ever before, was innovation. There was a lot of talk about automated and autonomous vehicles. And there were two great workshops on work zone ITS. In particular, I moderated a session Monday morning entitled, “Jump Start Work Zone Intelligent Transportation Systems in Your State”.

It was very well attended, 15 state DOTs were represented along with several local agencies and contractors. The material presented was fresh, and a very lively discussion followed afterward. The workshop looked at new and innovative ways states are contracting for work zone ITS in general and queue warning systems in particular.

Jerry Ullman of TTI led off by talking about the Texas model for contracting for these systems directly with the system providers and outside of the normal project contracting process. Steve Kite of North Carolina DOT talked about his state’s plan for doing the same thing through something similar to a professional services contract.

Keith Roberts of Illinois DOT described what they have done to bid an on-demand contract in his district. They tried doing it in a couple of different but similar ways in two districts. It has been so successful that Illinois is now going state wide. Priscilla Tobias, the Illinois State Safety Engineer, has approved bidding on-demand queue warning systems for all 9 Illinois DOT districts.

The bid includes rental rates for sensors and portable changeable message signs by the day, week and month. This on-demand contract is intended to supply queue warning for projects where the traffic impacts are short term, or unexpected. It could also be used for major incidents. Large projects requiring queue warning already include these systems as a line item and won’t normally use the on-demand rentals.

The obvious advantage to this method is you only pay for the system when you need it. There is never a need to justify use of a queue warning system until the queues develop. And then you order the number of devices you need to address the problem. It really is a more economical use of funding.

Another less obvious advantage is the agency works directly with the system supplier. Communication is faster and more seamless. DOTs learn the system capabilities faster and more completely and make better use of them as a result.

Many other states are now going forward with their own on-demand contracts including Indiana, North Carolina, and Michigan. And given the number of states that attended this session, don’t be surprised if several more join them very soon.

On-demand queue warning has revolutionized work zone ITS. It makes it available when and where it is needed, not just on large projects where traffic impacts are anticipated. We all owe a large debt of gratitude to Jerry Ullman of the Texas Transportation Institute for pioneering this method and to Priscilla Tobias and Keith Roberts of Illinois DOT for perfecting it.

If you would like to learn more you can begin by downloading the Illinois District 9 specification Illinois spec.

TRB 2014 – Questions and Random Thoughts

Happy New Year! 2014 means the return of TRB’s Annual Meeting and the chance to find many new and better ways to make our roads safer. Unfortunately, I will not be there but I’d like to pose a few random questions and comments for those of you who plan to attend. In particular I’d like to focus on Session 253 scheduled for 8:30 Monday, January 13th. It is entitled “Work Zone Traffic Control for Safety & Mobility”. Twenty-one papers will be presented during this session. I would like to focus on six of them.

14-1020 Work Zone Deployment of Variable Advisory Speed Limits

The hardware side of this is easy to do. It seems like the algorithms are what hold it back. What have they learned about changes to the speed limit that positively affect speeds and throughput? Is this still a new and relatively unproven system? Or is it ready for wider application?

14-1022 Effectiveness of Work Zone ITS

It’s not clear from the paper description what sorts of systems were evaluated, but I am hoping they will provide definitive cost/benefit numbers. We have all wrestled with performance measures. It is time to pick a few and use them until something better comes along.

14-2186 Using Private Sector Travel Time Data for Project-Level Work Zone Mobility Performance Measurement

I suspect this doesn’t work well. Private sector data is used to measure overall system performance, not localized work zone performance. It looks at mobility over many miles rather than through a work zone that is at most a few miles long.

14-3840 Work Zones Versus Nonwork Zones: Risk Factors Leading to Rear-End and Sideswipe Collisions

In work zones both types of crashes result most often from sudden stops and lane changes to avoid unexpected queuing. 26% of all fatalities in work zones are the result of end of queue crashes. Side swipe crashes come a close second. This is low hanging fruit for the work zone ITS world. We should be using technology to smooth traffic flows through work zones and reduce these crashes.

14-4109 Lane Bias Issues in Work Zone Travel Time Measurement and Reporting

I wonder, is this is related to placing sensors on the shoulder or in the median near the slow and fast lanes? That would form a bias if you did just one or the other. Do they recommend doing both? Or are they advocating measuring all lanes? That would be great, but any measurement is better than what we have in most work zones today.

14-4719 Queue Warning & Travel Time Estimation Near a Work Zone

As I said earlier, this is low hanging fruit for work zone ITS. Both are proven, easy and inexpensive to do now. And no matter what your goal is – improved safety or improved efficiency – there are benefits to both. I hope the presenters from SRF focus on moving these systems forward, rather than just describing how they were used in the past.

If you happen to attend this session, I hope you will let me know what is discussed. I am looking forward to reading all six papers when they become available. I am sure we will get into more detail at that time.

Enjoy TRB, and best wishes for a prosperous and safe 2014 to you all!