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!

One thought on “Queue Warning Systems

  1. Pingback: The Work Zone ITS Blog Through It’s First 18 Months | workzoneitsblog

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