A North Texas Tollway Authority bank account contains more than $57,000 collected from customers who have overpaid their ZipCash bills.

The North Texas Tollway Authority is quick to send drivers a bill for using toll roads in North Texas, but the agency is not so fast in tracking down customers when it owes them money.

An NBC 5 investigation has discovered that money from drivers who overpay on ZipCash bills is deposited into what the NTTA calls the Overpayment Account -- not refunded or credited toward a future trip on a toll road.

The NTTA has not previously made the bank account public. It contains more than $57,000 collected from ZipCash users who have overpaid.

NTTA toll roads are cashless. Drivers without TollTags are billed by ZipCash, the agency's pay-by-invoice system.

The NBC 5 Investigates team filed an open records request to find out how many people have money sitting in the account. The list of names is more than 950 pages long.

The list NTTA provided to NBC 5 Investigates did not include any identifying information beyond the drivers' names.

Haskell Tilson's name appears on the list. NBC 5 Investigates got Tilson's license plate number and sent it to the NTTA to confirm that he is the same person with money in the overpayment account.

Tilson's $2.22 in the account is certainly not a lot of money, but he said it's the principle that concerns him.

"Why don't they just credit it to the next bill or be honest about it and just send me a check for $2.22?" he said.

While the agency spends money sending bills to collect small toll amounts, the NTTA doesn't want to spend money to send out small refunds.

"And if that costs more to return it, we can't be using dollars to chase dimes," NTTA spokesman Michael Ray said. "That's not a good use of toll-payer money. They expect us to be good stewards of their money."

Watch NBCDFW.com's video report on the toll authority

Drivers have no way of knowing if their money is stuck in the overpayment account. Even though NTTA posts lists of people who owe the most in tolls, it has never publicly shared the list of people stuck in limbo.

NBC 5 Investigates asked Rey why the NTTA won't post the list and let people know about the account so they can call and ask that the money be credited to their ZipCash account.

"Well, because I think it makes good financial sense not to be starting a conversation over money that would cost us more to refund than it would be to send," he said.

While the money sits in the NTTA's hands, the agency is collecting interest on the $57,812.42 currently in the overpayment account.

The NTTA said it would refund money to customers with more than $2.50 in the overpayment account. But NBC 5 Investigates found that more than 1,500 people who are owed more than $2.50 have not received a refund or credit.

The NTTA claims it did not have enough information to find those people or set up an account for them.

If the money isn't claimed within three years, it will be sent to the Texas State Comptroller's unclaimed property division, which may ultimately notify people about their missing money.

The comptroller publicly posts a list of people with money in its account.

The tollway authority said it's just not worth the agency's time to post its own list because most of the people on the list are owed only pennies.

"And, honestly, that's what this is -- it's a lot of nickels and dimes, a lot of pennies and two cents," Rey said.

The NTTA says there is currently $57,812.42 in the overpayment account.

Search the NTTA overpayment database

The account was created in August of 2009. But the NTTA has only provided NBC 5 Investigates with a detailed spreadsheet documenting transactions from May 2010 to Nov. 26, 2012.

Customers who find their names on the list can call the NTTA customer service center at 972-818-NTTA (927-818-6882). The agency says it will credit the money to their account if the customers can provide proper identifying information.