Every driver in Michigan has driven over these black cables/tubes while driving in Michigan. These cables are being used for something. Is Michigan using these cables to bust drivers for speeding? These black tubes on Michigan roadways do more than that, they're high tech.

What are these tubes called?

The tubes that you see on the streets or highways in Michigan are called pneumatic road tubes. The Federal Highway Administration breaks down what these are used for.

Principles of Operation

Pneumatic road tube sensors send a burst of air pressure along a rubber tube when a vehicle's tires pass over the tube. The pressure pulse closes an air switch, producing an electrical signal that is transmitted to a counter or analysis software. The pneumatic road tube sensor is portable, using lead-acid, gel, or other rechargeable batteries as a power source.


Applications and Uses

The road tube is installed perpendicular to the traffic flow direction and is commonly used for short-term traffic counting, vehicle classification by axle count and spacing, planning, and research studies. Some models gather data to calculate vehicle gaps, intersection stop delay, stop sign delay, saturation flow rate, spot speed as a function of vehicle class, and travel time when the counter is utilized in conjunction with a vehicle transmission sensor (JAMAR Technologies).

The information that these tubes gather helps MDOT make solid decisions when it comes to construction on our roadways. Without these tubes there wouldn't be any real data to analyze when it comes time to make decisions about road construction projects throughout the state of Michigan. If you "pucker" each time you cross one of these, maybe you should slow down.

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Gallery Credit: Laura Hardy

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