BROOMFIELD, Colo. — A tolling error that lasted nearly two weeks along U.S. 36 has resulted in about $3,600 in refunds to drivers.

If you have used one of the new “dual position” toll passes for U.S. 36 in the past month, you might have noticed a small credit to your account.

One of the electronic Express Toll readers located above the eastbound toll lane at Sheridan Boulevard and U.S. 36, wasn’t working right. The mistake went undetected from Aug. 13-24 because of human error.

“The problem that we had is we got two error messages seconds apart,” said Terry Ostrom, a vice president for Plenary Group, which operates and maintains the highway. “We thought it was the same error. We fixed one of those, we didn’t fix them both.”

The error was eventually discovered thanks to the watchful eyes of a customer.

“The customer that called, the toll was only 50 cents,” Ostrom said. “Some people might say, ‘I’m not going to call for 50 cents.’ But she did call.”

And that call added up to savings for roughly 3,600 drivers. Each customer received an average refund of about $1.

In reality, only about 500 carpool drivers were likely shortchanged, but many more drivers are going to benefit from the mistake.

“So, in other words, everyone got a credit because we couldn’t tell if you had driven through as an HOV or a tolling customer,” Ostrom said.