Next time you’re on the highway or a residential street, pay careful attention to the road.

At some point during your trip, chances are you’ll see black cables either carefully placed on the ground. While they’re perfectly safe to drive over, what purpose do they serve?

Road tubes are a simple and easy way for local transportation agencies to gather important information about an area’s traffic patterns. They’re typically placed in unassuming areas so they cause the least amount of interference. Any time a vehicle’s tire hits the tube a burst of air is sent through the rubber tubing to the on-site counter, which collects all the data. Once the tubing and counter have been in place for a predetermined amount of time, the data is collected and interpreted. Not only is the tubing counting cars, but it can determine peak traffic by analyzing the interval between air bursts. When the tubing is used in pairs it can provide even more data like vehicle class, speed, and direction. This data can then be used any time an agency needs to determine if speed limits need to be changed or signage needs to updated.