You may run into some mysterious black cables on the road this Thanksgiving holiday.

A lot of us are traveling this week and if you have kids or are an expert procrastinator, you may be running late. Besides flying, we'll likely run into traffic jams, busy interstates, and of course people who apparently ran out of blinker fluid.

Because nothing says being thankful quite like busy roads.


You may have seen a few roads that have 2 parallel black cables across a part of it. They look like this:

South Carolina DOT
South Carolina DOT

I've ran over them before and just thought to myself "well oops hopefully those weren't sharp" and just kept going on my merry way. Especially now around the holidays and holiday travel, there's a good chance you'll encounter these so what actually are they?

What The Black Cables Do

Mental Floss says they're actually called 'pneumatic road tubes'. They basically measure your speed and traffic. Every time a car's tires hit the tubes, they release a burst of air that triggers a switch that produces an electrical signal that's recorded by a counter device.

But it's not really something you need to worry about. It's using that data more internally for the DOT and city to keep track of traffic patterns, like if a speed limit in a certain place is working. A few years ago in Cedar Rapids, the cables were used to make the “Average Annual Daily Traffic” count by the Iowa DOT.

It makes sense for DOT's to put them out around this time as it helps with long-range planning, figuring out traffic patterns from year-to-year, and maybe helping resolve congestion issues, according to Independent Mail.

So if you go zooming over a pair of them on your way to your relative's house this week, it's probably not the end of the world.

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