Have you ever seen those cables strung across the street, going to a box on the side of the road and wondered just what is going on? Should you be worried about a speed trap or tipping the cops off to your speeding habits on this particular road? Not exactly, but there is a lot the DOT can glean from these cables.
First off, the cables are called pneumatic road tubes, which is fun to say, and gives you a hint of how they work. The tubes count each time the pressure of a car's tires go over them. This can give engineers useful insight into how much traffic is on a particular road. Put two tubes across the street with a gap in between, and now speed and direction is also able to be determined. This data helps engineers make a number of decisions.
In this video, Donut Media looks at speed limits in depth, but right at 1:53 is where the cables come in to play.
Engineers can use the average speed of a road to determine a reasonable speed limit. The traffic count can give insight into many different traffic studies, including if lanes need to be added to keep up with increased use. Since, in the US at least, these cables are often for temporary traffic studies and not tied to a live feed or any sort of camera, there is little risk that the speed recorded will be tied to your car and result in a ticket.
But better safe than sorry right?
Related: Here’s why the edges of your windshield are covered in tiny black dots