HARRISBURG — The cash toll for a cross-state trip on the Pennsylvania Turnpike is expected to reach about $50 by 2021, state Auditor General Eugene DePasquale said Tuesday as he urged lawmakers to halt the spiraling debt resulting from the massive contributions the turnpike is required to make toward the state’s other transportation needs.

Legislators are considering a major expansion of transportation spending in Pennsylvania and there appears to be general agreement that any final plan should gradually eliminate the Pennsylvania Turnpike Commission subsidies. But there is no consensus on some details, including the length of a phase-out.

“The longer it takes to phase out that debt, the more expensive it will be,” DePasquale, a Democrat who took office in January, told the House Transportation Committee.

DePasquale presented a report that documents how the annual transfers of hundreds of millions of dollars from the turnpike to the Pennsylvania Department of Transportation that began in 2007 are forcing significant increases in tolls and hurting the turnpike’s financial condition as it borrows money to make the mandatory payments.

As of May 31, the turnpike had paid out $3.9 billion that was financed by $4.3 billion in debt, he said.

The auditor general noted that all three major credit rating agencies — Moody’s, Standard & Poor’s and Fitch — have downgraded the turnpike’s bonds since the 2007 law was enacted.

The turnpike’s total debt obligation, excluding interest, increased from $2.5 billion in 2007 to nearly $8 billion last year.

The turnpike payments are a holdover from a 2007 law that dedicated billions of dollars to the state’s roadwork and bridge repair needs and authorized the turnpike commission to collect tolls on Interstate 80. Federal regulators rejected the I-80 tolls, but the law continues to require the commission to transfer $450 million a year to PennDOT through 2057.