Demolition experts will use explosives Friday morning to bring down the last two sections of the old Pennsylvania Turnpike bridge over the Allegheny River.

The blasts are scheduled for 10 a.m., according to the turnpike commission.

Most of the old bridge had been imploded on July 13.

The old bridge and the $193.6 million twin spans that will replace it carry turnpike traffic between Plum and Harmar.

As part of the preparations for Friday's demolition work, the stone-and-concrete abutments and piers that supported the old bridge are being dismantled. Former Allegheny County Councilman Dave Fawcett had lobbied the current council to take ownership of the piers, but county officials ultimately declined.

Mr. Fawcett argued that the old bridge supports could provide the foundation for a future biking-hiking trail across the river. Such a structure could become an important element in a riverfront park that would link the county's four major waterways: the Ohio, Allegheny, Monongahela and Youghiogheny rivers, Mr. Fawcett said.

Turnpike spokesman Tom Fox said the county "notified us that they're not interested [in the piers] and so we're proceeding."

When county council debated the issues of the piers at its July 6 meeting, several members warned that the county would be taking on too much liability for future maintenance and accidents if it accepted them. Council then asked the administration of county Executive Dan Onorato to review the issue and make a recommendation, council President Rich Fitzgerald said.

Time was too short and too many questions remained unanswered for the county to agree to take ownership of the piers, a spokeswoman for Mr. Onorato said Wednesday. The proposal was reviewed by the county's law and public works departments, Megan Dardanell said.

Friday's demolition involves a 268-foot-long steel section on the western, or Harmar, end of the turnpike bridge and a 213-foot-long section on the eastern, or Plum, side of the old span. The steel trusses on the western side are expected to fall into a back channel of the Allegheny that is not used by river traffic. The steel on the eastern side will fall on land used by the Allegheny Valley Railroad.

Fourteen residences will be evacuated during the demolition and a 1,500-foot safety perimeter will be set up around the implosion site. Traffic will be stopped on the turnpike at mile 46.5 eastbound and mile 49.5 westbound before the blast. A portion of Freeport Road also will be closed, as will Denny Estates in Harmar.

The old bridge, the third longest span on the turnpike, was completed in 1951.

Its replacement is a double span 2,350 feet long that will carry three lanes of traffic in each directions when completed in November. One of the new bridges opened in October and is temporarily carrying traffic in both directions.

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