Cameras or Sensors?

I don’t claim to be an expert on this subject. In fact, I hope to learn more about it from you. But I believe that when you are budgeting your work zone ITS, you are almost always better off putting most of the money into sensors rather than cameras. You only need so many cameras and you probably don’t need any at all. But I’m not sure you can have too many sensors.

In my experience, cameras cost at least three times more than sensors. The device itself is more expensive because it needs a larger trailer, more solar and batteries to power it, and a taller tower. It also costs more for wireless service because it requires much more bandwidth and it requires it continuously, not just for short packets of data. In some cases cameras cost more than 5 times as much as sensors. So, for your money, you can get three to five more sensors for every camera you give up.

We need to better understand both tools before we can discuss the budget. When do we need cameras? Most of the time cameras are used to verify the data from the sensors. Is traffic really stopped? Or was this a false reading? But if you have enough sensors, the ones on either side of the one you are verifying will quickly do it for you. And, they will do that automatically. Just because we can check the data obsessively doesn’t make it a good idea.

But this is not to say we never need cameras. There are some good reasons to have them:

  • Publishing video to a webpage helps drivers check conditions quickly and raises public awareness about the work zone.
  • Emergency response may be improved by viewing the incident first to know just how bad it really is and to direct responders to it in the most efficient way.
  • Some DOTs may want a video record of the work zone traffic control. This is still controversial but whether you agree with the idea or not, it is still a legitimate reason for cameras.

A reason that is less legitimate is the use of cameras to look at ongoing work or to look at locations on the jobsite without having to drive there. This does save time and money, but not enough in itself to justify the cost.

These are some of the questions you should ask yourself when evaluating the need for cameras:

  • Are there permanent cameras at or near the project that can be used?
  • Is the job several miles long? The longer the project, the more important video becomes to groups like emergency response.
  • Will there be several stages to the work? As construction progresses and traffic control is changed, it is important for drivers to know about those changes in advance.
  • Is public outreach a part of your TMP strategy? If so, a web page with video might be an important tool.
  • Will there be lane shifts, narrow lanes, or a significant reduction in capacity during construction? Any of these conditions may result in an increase in collisions. The more problems you expect, the easier it is to justify the expense of cameras.
  • Is this what FHWA calls a “major” project? The larger and more complicated the job, the more likely you are to benefit from CCTV.

Cameras have their uses. But next time you are planning a job, please ask yourself these questions and consider your goals for work zone ITS before you decide to add them to the project. You may be able to do the same thing more efficiently by just using sensors. What do you think? Have I left out important questions? Is there a side to this I have not considered? Make your comments now and keep the discussion going!

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