What are the black tubes that run across Texas roads?

TEXAS (KXAN) — Those traveling across Texas have probably seen — and driven over — a slew of black cords running across roadways. But what exactly are they, and how are they used?

The U.S. Department of Transportation’s Federal Highway Administration (FHWA) calls them “pneumatic road tubes,” an in-roadway sensor that can help detect and track vehicles traveling on roads. They’re typically used as short-term traffic counts, with some models having the ability to gather data related to the following:

• Gaps between vehicles
• Intersection stop delays
• Stop Sign delays
• Saturation flow rate
• Spot speed
• Traveling time

Alongside their uses in short-term traffic counts, they can be used to detect vehicle classification (via axle count and spacing) as well as assist with planning and research studies. But how, exactly, do they work?

How does it work?

The tubes are portable and are placed perpendicular to the direction of the traffic flow. When a vehicle’s tires drive over the tube, the tube’s sensors “send a burst of air pressure along a rubber tube,” per the FHWA.

That air pressure pulses close to an air switch, which is able to create an electrical signal that’s then sent back to a counter or analysis software synced with the tube.

Here in the Lone Star State, the Texas Department of Transportation collects roughly 82,000 short-term traffic volume counts each year along with approximately 1,000 vehicle classification counts, per its traffic count maps database. Among those counts collected, nearly half of them — 46.9% — are used to track traffic volume, according to the database.

The state department has more than 300 permanent count locations across Texas that collect data around the clock. KXAN reached out to TxDOT to confirm how many pneumatic road tubes are used as part of those traffic data collections. We will update this story once we’ve received a response.