HOUSTON -- The EZ tag lanes on Harris County toll roads are designed to make it fast and easy to pay a toll. But the KPRC Local 2 Troubleshooters discovered not paying could cost a lot more than you might think. Amy Davis uncovered the hidden fees and fines that can turn a petty toll road dodger into a dodger in debt.

Keesha Jones has a busy job greeting drivers and collecting cash at a tollbooth as drivers pay their way.

While some wait in line, others "throw and go." Eighty percent use an EZ tag to pay the $1.25 toll.

But thousands of drivers on Harris County toll roads are not paying a dime.

How can running just a handful of tolls end up costing hundreds, or even thousands of dollars?

"There's always an element of surprise associated with it," said Tracy Smith, manager of violation enforcement for the Harris County Toll Road Authority.

It was a big surprise for driver Sonny Willis.

"I think the total of the tolls was somewhere around $40. But I think the total with the administrative fees was somewhere around $400," he said.

Not paying at the tollbooth costs much more than the price of the toll. Here's why.

Paying your way at three tollbooths costs $3.75.

But if you're caught not paying at those same three booths, you would pay a $33 administrative fee added to the $3.75 toll cost.

If the fine is not paid in 30 days, another fine of $42 is added.

So, the total for three tolls turned into $78.75.

"For every third violation within a 12-month period, a notice is sent out," Smith said.

And, for every third violation notice, another set of fees is tacked on.

So, if you run those three booths every day during a workweek, 15 unpaid tolls could cost $393.75.

Run those three booths for one month and you could owe $1,575.

Every year, constables round up repeat violators -- some of whom owe tens of thousands of dollars in tolls and fees.

Violators who don't pay also cannot renew their vehicle registration.

But why are the fees so high?

"We have to be able to take care of the operational expenses, the court expenses. There's not really a valid excuse for violating the toll," Smith said.

"I think it'll get their attention. We're talking 10 times what the toll would cost -- it's not worth it," Willis said.

The good news for Willis -- his 40 unpaid tolls was a paperwork mix-up. He will only have to pay $40, not $400.

The Toll Road Authority said that violators are not charged anything if they don't run more than three tollbooths in a year. That way, an honest mistake won't cost anything.

And, even big-time violators have a chance to negotiate smaller fines and fees.

Every week, 250 violators get that chance in a special court set up for toll road fines.