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!

Maintenance and Work Zone ITS

If you are considering including a work zone ITS system in a project, there are many factors you should consider. First and foremost you should be certain the system you choose will achieve the desired results. Data quality, data format, and real time data availability are all very important. But a third area should also be evaluated: how quickly can your vendor respond when equipment is damaged, stops working correctly for some other reason, or when it must be relocated.

Work zone ITS has come a very long way in quality and dependability in a few short years. But the equipment is still placed near traffic where accidents occur. Hardware can and sometimes will fail. If you include enough sensors, the failure of one is probably not an emergency, but it should be repaired or replaced quickly as the system response won’t be as good as it would be with a full set of sensors.

A more likely issue is data. The sensors may be working as intended, but due to location may not be sending data that fits your needs. For example, you may find it is picking up slow moving vehicles because it is on a steep hill, or near a weigh station offramp. Perhaps the traffic control is causing traffic to slow at that location briefly before going back to full speed. In any of these cases you may need to move the sensors to a better location so the system does not send out false alarms.

Construction activity can also cause issues. Workers may move a sensor out of their way as the paver moves past it, and then move it back once they are beyond it but without aiming it properly. The sensor shows there is no traffic because it is pointed at a flock of sheep rather than at the road. Or slow moving construction equipment, if detected by the sensors, will trigger false alarms.

This varies with the type of sensor as well. Some require more frequent attention than others. Simple radar is more forgiving. Side fire microwave sensors like Wavetronix or RTMS must be aimed precisely and calibrated at each location. Wind and vibration cause sensor trailers to move and can affect the output.

So it makes good sense to require local service and support. What the response time must be will vary greatly from project to project. Problems with one device in a travel or delay time system probably can wait for a day or two. But a sensor out in a queue warning system for a blind curve must be corrected much faster – usually in less than a few hours.

Be very specific with your expectations.  Let everyone know going in what the maximum allowable downtime is for each device, each feature and for the software and server controlling them. That time will vary by device. The server and software must be up and running 24/7. Sensors are probably the second most important. Cameras and message boards are next. Alarms to users are probably last.

Consider including damages for downtime beyond the allowed maximum for each device and for the system as a whole. The number you choose should be a reasonable percentage of the total system cost. It might be the cost per day charged by the vendor for that device if that cost is known. Or you might use the system cost per day divided by the number of devices (less some percentage for the software, server and website). The important thing is to make both your expectations and the consequences if they are not met very clear to all concerned before the project bids. Then the vendor will know his or her costs going in.

But however you choose to define your requirements, be sure to include local representatives on call and available to make the little adjustments every system needs to operate at peak performance.

Queue Warning Systems

You are probably familiar with the term “low hanging fruit”. It refers to the easy items on your to-do list – those you can complete with very little effort and which are almost certain of success. In the world of work zone ITS the item at the top of everyone’s list of low hanging fruit should be queue warning systems. I say this for several reasons:

  1. The technology is proven, mature, and available everywhere.
  2. It is easy to use, and easy to maintain.
  3. These systems cost very little.
  4. The benefits are HUGE! 26% of all work zone fatalities occur as a result of end of queue crashes. Any measureable reduction will put a big dent in a state’s work zone fatality numbers.

Many states already recognize this and are requiring these systems for any project where dynamic queuing is anticipated. They don’t have to be major projects. In fact, queue warning benefits small to midsize overlay projects more than any other. There the queues are unpredictable. The job location moves daily so even the locals are often surprised by it.

These systems consist of one or more traffic sensors upstream of the work. Usually these are spaced a half mile to a mile apart. In rural areas that spacing might be increased. The sensors send the data in real time to a server. When slow or stopped traffic is detected, the server triggers a warning on one or more portable changeable message signs further upstream. All of that takes place in seconds.

Drivers pay attention when you tell them SLOW TRAFFIC AHEAD / PREPARE TO STOP. And if they drive that route regularly they will soon appreciate the timeliness of the warnings.

If you decide to use them in your state, there are a few things I recommend:

  1. Always place the first message sign (the one farthest from the job) well upstream of any potential queuing. You don’t want the traffic to back up beyond that sign.
  2. Most systems accommodate three sets of messages: a standard, free-flow message (CAUTION / ROAD WORK AHEAD); a slow traffic message (SLOW TRAFFIC AHEAD / PREPARE TO STOP); and a stopped traffic message (TRAFFIC STOPPED AHEAD / PREPARE TO STOP). For freeways and highways posted at 55 MPH or higher, try setting the trigger speed at 45 MPH for the slow traffic message and at 25 MPH for the stopped traffic message. These are average speeds so one slow tractor won’t normally trigger the warnings.
  3. Watch the results. You may need to adjust the trigger speeds, or the sensor spacing, or the message sign spacing. No two jobs are alike, but you will quickly learn what works best in each situation.

Sensors rent for no more than message signs in most cases. So a system like this will cost no more than twice what you were already planning to spend for “dumb” message boards and it will be far more effective. Queue warning systems are proven to significantly reduce both the number and severity of rear end crashes. ..that’s low hanging fruit for sure!

The Dumbing-Down of “Smart Work Zones”

We talk a lot about smart work zones here so we take it for granted that everyone knows what we mean when we use that term. But apparently many do not. Several states are now requiring smart work zones on projects, but their specifications only show the number of message signs required. The messages on those signs are then changed manually as needed by the TMC. So the only thing that is “smart” about their work zones is the modem in the message signs.

There is so much about this that bothers me! A contractor is being paid to supply a full system, yet is only supplying signs. This cheats taxpayers and road users and results in a far less safe work zone. It will also be more difficult to convince decision makers to include work zone ITS elements in future projects.

The signs are updated manually from the traffic management center. Most TMCs are not staffed 24/7 so the “system” only works when someone is there to operate it. If the DOT chooses to staff the TMC for this purpose they are paying far more than it would cost to automate the process as was originally intended.

They are using existing ITS elements to monitor traffic through the work zone. Most DOTs say that about 20% of permanent loops, sensors and cameras are off line or out of service at any given time. Even on a very well instrumented stretch of roadway, this would leave unacceptable gaps in coverage for most work zones. To react quickly to slowing or stopped traffic you need sensors spaced a half mile to at most one mile apart. At freeway speeds you will then learn of slowing less than a minute after it begins.

And, most important of all, humans cannot react to events and change the signs as quickly as software does. That leads to more secondary crashes, slower EMS response, and longer delays for the folks driving through these work zones.

These states need to tighten up their specifications immediately. There are many good examples of work zone ITS specs available now. Gerald Ullman of the Texas Transportation Institute recently developed a great one for TxDOT. Scott McCanna at Oregon DOT also has a good one. But whatever states choose to use as a specification it must include either specific numbers of sensors, or very clear performance measures regarding event detection and response.

In the meantime, as the torchbearers for work zone ITS, we need to explain what devices and software a work zone must include to be called “smart”. If we do not, we will have only ourselves to blame for the dumb results.

Should States “Do-It-Yourself” for Work Zone ITS?

At the same peer-to-peer exchange in Iowa that we have been discussing for the past month or so a good friend told me he believes state DOTs should just buy or rent the hardware to gather work zone data and integrate their outputs with that state’s existing TMC system. Caltrans has done the same thing in District 7 – Los Angeles.

This seems to make good sense on the face of it. Why, they ask, should you pay for the “same” software twice? You already have good system operations software that measures traffic flow and sends that information to 511, websites, variable message signs, and more. They also argue that TMC operators don’t want to (or won’t) toggle back and forth between two software packages.

But when you look into it further you find this path is filled with problems.

First, you learn the software is not the same at all. Systems operations software measures and acts upon traffic flow at the system level. It looks at it from a regional or state perspective. It does not “zoom in” to the project level to find and react to queuing or slowing occurring in a specific work zone.

This goes back to my earlier post regarding the difficulty of explaining the value of detailed work zone data to systems operations folks. We know it is important to know where the slowing occurs. Then we can make adjustments in our traffic control to maximize throughput and safety.

The other important aspect of this is the need to learn about problems immediately. By doing so we can react quickly to eliminate or at least minimize the problem causing the slowing. This increases throughput, greatly reduces secondary collisions, and improves safety.

Another problem is the equipment itself. Someone must maintain it. And new improved equipment is introduced every month.  Software is evolving in our industry but hardware will continue to make quantum leaps in design, functionality, expense, communications, and areas we have not even considered yet. So it just doesn’t make sense to tie up precious dollars in equipment that may just sit in the DOT yard.

The third important problem with this procurement method is that work zone ITS elements move. That is by design. Someone must watch that to be sure the system is working properly. Also, most system operations software does not take this into account. They don’t normally offer robust GPS device tracking. So anytime a sensor is moved, for example, someone must manually update the gui maps, and system location information.

I understand where this strategy is coming from. The DOT wants to use more work zone ITS on their projects but they haven’t found a satisfactory way of getting both competitive bidding AND a system that performs to the specification. I think we will learn how to do that in time. Meanwhile it is far better to jump in and try things. Learn what your needs truly are and then you can put a better specification together next time. And make this the responsibility of a contractor who will focus on the system for one particular work zone to get the best possible performance at that location.