By Pat Loeb

PHILADELPHIA (CBS) – Have you ever noticed a big truck riding your bumper as you go through an E-ZPass toll? If so, you better check your statement right away. The truck could be trying to get a free ride on your dime.

Certain toll gates don’t detect the space between vehicles if it’s small enough, so a truck close enough to the car in front can sneak through, while the car gets charged as a commercial vehicle.

The New Jersey Turnpike and Delaware Toll use more sensitive equipment which doesn’t allow it to happen, but Tim Ireland of the Delaware River Port Authority says it is an occasional problem on its bridges.

“We don’t keep statistics, but it’s pretty infrequent and there’s a reason it’s infrequent; it’s very risky for the trucker who does it,” such as the potential danger of a sudden stop by the car ahead.

Ireland says there are stiff penalties when drivers are caught.

“We’ve actually had grown men cry because we’ve impounded their trucks.”

Anthony Curtis drives a five-axle truck. And, though he says he pays all his tolls, he understands drivers who try to get around them.

“If you come off the NJ Turnpike, the toll is $25. This stretch here is $9. So, do your math. You dropped $34 for 17 miles.”

A frequent commuter, gassing up on I-95, says it’s a good idea to keep an eye on E-ZPass charges.

“This is the first time I’m hearing of this but I’ll certainly be mindful of it going forward.”

PA Turnpike officials declined comment.