The Delaware River Port Authority dipped into its general fund to help pay off nearly $100 million of its debt last month.

That dropped the agency's outstanding debt to $1.2 billion, but that figure will grow later this year, as the DRPA expects to borrow up to $400 million for long-term upgrades to its bridges and railroad, agency finance officials said Wednesday.

The DRPA operates four toll bridges over the Delaware River and the PATCO commuter rail line.

The agency's debt has been a concern for years. More than 40 percent of bridge tolls go to pay principal and interest on it, significantly more than at other regional toll authorities.

Part of the debt is due to the DRPA's controversial economic-development spending. Over the last 15 years, the agency spent about $500 million for such things as concert halls, sports stadiums, museums, and monuments, prompting criticism from motorists and politicians on both sides of the river.

Chief financial officer John Hanson said Wednesday that the DRPA paid $95.7 million of its debt in April, using $85 million from the general fund and $10 million from the debt-service fund created for that purpose. The move will save the agency about $3.2 million in interest payments over the next eight months, he said.

The debt will rise again in the fall when the DRPA goes to the bond market to borrow for capital projects, such as bridge repairs and refurbishing PATCO rail cars.

Contact Paul Nussbaum at 215-854-4587 or pnussbaum@phillynews.com.