Just about every driver has driven across what looks like a pair of black rubber hoses stretched across the pavement. But do you know what those are actually for?
They aren’t abandoned construction material or speed-enforcement equipment put in by law enforcement. Transportation departments and local governments use them to collect information about how vehicles are using a road.
Learn how the tubes work, what data they’re collecting, who is collecting the data, and what drivers need to know before driving over them.
What the Black Tubes Measure and How They Work
Those black tubes, often called “pneumatic road tubes,” connect to a small counter positioned nearby that tracks when vehicle axles pass over them. When a vehicle rolls over a tube, the tire compresses it and sends a change in air pressure toward the counter.
The Federal Highway Administration (FHWA) describes pneumatic road tubes as a common option for short-term traffic counts and vehicle classification.
“Road tube sensors are usually low cost and simple to maintain,” according to the FHWA. “Sensor manufacturers often supply software packages to assist with data analysis.”
Crews may install one tube or several in different configurations depending on what they want to measure. A single tube can record axle hits that agencies use to estimate traffic volume. Two tubes can provide more information, including vehicle speed and direction. The spacing between axle hits can also help the equipment classify different types of vehicles.
The tubes don’t track other vehicle or driver information like license plates, vehicle make and model, driver identity, or photographs. Crews can also install and remove the portable equipment fairly easily once the data collection period has ended.
Why Transportation Agencies Use Them
Road tubes are used by transportation agencies across the United States, and each agency may collect the data for different planning or traffic studies.
For instance, the Alaska Department of Transportation and Public Facilities uses traffic counters to collect information that helps with transportation planning. Local governments may use the same equipment while reviewing neighborhood traffic. The City of Chandler, Arizona, includes road-tube sensors among the tools it uses to study traffic volume and speed.
The data gives civil engineers a clearer picture of how a road is being used when they’re working on planning or safety reviews.
What Drivers Should Do When They See Them
If installed correctly, drivers have no reason to worry about pneumatic road tubes other than perhaps the slight sound or bump when going over them. The tubes are designed to sit across travel lanes while vehicles pass over them without interrupting normal traffic.
Drivers should follow normal road rules and shouldn’t brake suddenly or try to drive around the tubes. So the next time those black tubes appear across the road, they’re likely helping a transportation agency understand how traffic is moving through the area.
Sources
Federal Highway Administration, “Pneumatic Road Tube”
Federal Highway Administration, “Traffic Monitoring Guidebook, Chapter 4”
Alaska Department of Transportation and Public Facilities, “Traffic Counters”
City of Chandler, Arizona, “Traffic Volumes and Calming Measures”
Town of Abington, Massachusetts, “Traffic Counter Notice”
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