PITTSBURGH -- The transit agency building a light rail tunnel under Pittsburgh's Allegheny River said work will continue.

The tunnel project will extend the Port Authority of Allegheny County's 25-mile light rail line from downtown to the North Shore, where Heinz Field, PNC Park and a planned slots casino are located.

Transit officials said rising construction costs have added $118 million to its $435 million price tag. The tunnels were finished last month, but workers must still install tracks and build new passenger stations.

Port Authority officials are recommending awarding contracts for two new phases of the $552 million project.

The new contractors would include work for the train systems, including tracks, power service and signals, as well as a package for elevators and escalators at the new stations.

Project leaders are encouraged by the new stimulus bill signed into law this week.

"There's been a 36 percent increase in construction material, so that's been the driving force behind the cost increases," said Steve Bland of the Port Authority. "Right now, our job is to make sure we carry out the project safely, do the scope well, and keep costs under control."

Transit officials said it would cost $21 million to seal the tunnels until money is available to finish the project.