PennDOT ordered the emergency closure of the Birmingham Bridge this morning due to an unexplained drop of up to 8 inches in a portion of the span over the Monongahela River.

The drop, apparently noticed overnight by a motorist who called 911, occurred on the span linking Fifth Avenue, Uptown, to the South Side. The inbound, or nothbound, lanes were likewise ordered closed, at 8:45 a.m., to allow for a comprehensive inspection of the entire bridge, which really is two independent superstructures.

Crews were working to shore up the western edge of the outbound span where the roadway had dropped 7 3/4 inches and on the eastern side by 2 1/2 inches.

PennDOT District 11 Executive Dan Cessna said a preliminary inspection indicated a girder beneath the bridge had slipped off a rocker bearing connected to a pier. The bearing allows the bridge to move when weather changes cause it to expand and retract. He said extreme temperature changes recently may be to blame for the girder's slippage, but he added that it was too early to say so with any certainty.

Should an inspection show that the inbound span is safe for vehicular travel, it likely will be opened to accommodate traffic in both directions, Mr. Cessna said. The bridge now carries an average of 23,000 vehicles a day.

PennDOT recommended motorists use the Hot Metal Bridge and the 10th Street Bridge as detours to connect to the South Side or Uptown.