HARRISBURG, Pa. (CBS) — Another 6-percent increase in Pennsylvania Turnpike tolls took effect Sunday morning. Concerned about the impact of annual toll hikes, the state auditor general says he will begin another audit of the Turnpike Commission.

In addition to funding its own improvement projects, the Pennsylvania Turnpike Commission – in keeping with a state law – has been borrowing and providing billions for other transportation needs. It has also raised tolls annually as a result. Auditor General Eugene DePasquale says that may be taking a toll on the Turnpike’s future.

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“I am very concerned that their projection when they laid out in our last audit how this was going to work, was they were going to keep raising tolls and traffic was going to keep going up,” he said. “I’m not convinced that’s going to happen.”

With the latest increase of six percent, the most common toll for a passenger vehicle – the minimum cost to travel from one exchange to the next — has jumped from $1.23 to $1.30 for E-ZPass customers and from $1.95 to $2.10 for cash customers.

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DePasquale said he’s concerned about the long-term viability of the Turnpike.

“Their belief from their consultants that…despite the increase in tolls, they would have increased traffic…and we’ll be analyzing if that was an accurate assessment or not,” he said. “Because, the concern is, you increase tolls to the point that you actually start losing revenue.”

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The Pennsylvania Motor Truck Association has warned that the rising cost of tolls will eventually force trucks off the Turnpike and on to side roads.