Two remaining structures of the old Allegheny River Bridge on the Pennsylvania Turnpike will be imploded at 10 a.m. Friday, the turnpike commission announced this morning.

A 268-foot span on the western side of the bridge will fall into the non-navigational backchannel of the Allegheny River and a 213-foot span on the eastern side of the bridge over the Allegheny Valley Railroad will fall on land. In addition, abutments on each end of the bridge and the eight piers in between are in the process of being dismantled.

Some had hoped to preserve the bridge piers for a possible future biking/hiking trail across the river, and the turnpike had agreed not to demolish them if Allegheny County would take ownership and responsibility. Turnpike spokesman Tom Fox said the county "notified us that they're not interested and so we're proceeding."

Debris from the first blast that fell into the river has been removed, the turnpike said in a news release today.

Fourteen residences will be evacuated during the demolition and a 1,500-foot safety perimeter will be cleared. Traffic will be stopped on the turnpike at mile 46.5 eastbound and 49.5 westbound and a portion of Freeport Road will close, as will Denny Estates.

Turnpike officials said there are no safe viewing areas around the bridge because of surrounding structures and private property restrictions.

The old bridge is being replaced by a $193.6 million twin structure, 2,350 feet long and 120 feet high, that will accommodate three lanes of traffic in each direction when completed in November. One of the new bridges opened in October and currently carries traffic in both directions. The main spans of the old bridge were detonated July 13.

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