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.