We've all seen them when we're driving right? Out of nowhere, we see these two random black cables just laid out on the road, whether it's on a city street or the highway.

The big question is what are they and what purpose do they actually serve? They only seem to pop out like once, maybe twice a year.

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The purpose of these black cables, or tubes, is to keep track of just how much traffic is rolling through a certain area. Sure, we can guestimate just how much traffic is moving through an area, and us as locals always know where the busiest places are, but they do more than just count cars.

It gives TxDOT an idea of what TYPES of cars are coming through the area as well. It gives them an idea if more buses, semi trucks, etc. are rolling through or if it's more commuter vehicles. It helps them determine what type of road work may need to be done now, or in the future based on the weight the road has to handle on a regular basis.


One question that comes up is do these cables, or tubes, monitor speed? Well, in fact, they do. No, they aren't connected to the police department and if you speed over them, you aren't about to get pulled over.

Tracking the speed gives TxDOT an idea of the average rate of speed vehicles are traveling on that particular road they are monitoring, which allows them to determine whether or not speed limits are predominantly being followed or if that higher (or lower) rate of speed is affecting how long the road will last.


Typically these cables, or tubes, are placed in the same locations every year. Hot spots are identified, and they try to see if those spots remain the same, or if traffic patterns have a tendency to change.

Every now and then, you'll see them pop up in spots you normally don't see them, but only if they feel they're becoming a hot spot for repair.

So when you see these cables, don't change anything you're doing in your car. No one is taking a picture of you speeding, they just want to make sure our roadways remain safe for us to be on.

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