An entire travel corridor just east of Downtown will be almost totally blocked for up to three hours early tomorrow morning as crews put a dislodged southbound span of the Birmingham Bridge back where it belongs.

The closings will start at 7 a.m. and include the Parkway East/I-376, Second Avenue and the Boulevard of Allies in both directions. The Pennsylvania Department of Transportation also will shut down Forbes Avenue, which is one-way outbound toward Oakland, and Brady Street, a city street to and from Second Avenue.

Fifth Avenue in proximity to those arteries will remain open, but it runs one-way inbound and will be part of a designated detour for westbound traffic diverted from the Parkway East.

PennDOT emphasized in its traffic notice that "motorists who choose to travel those routes should expect significant delays."

The best advice may be couched in its words. That is, if possible, choose not to venture anywhere near the Birmingham Bridge until officials give the "all clear" sign, despite the fact that traffic is pretty light on Saturday morning.

On the other hand, if all goes well, PennDOT said all the roads that pass under the north end of the bridge and its ramps could be reopened in less than one hour.

State and some city and county police are to be posted on the Parkway East and at some other key intersections during the closure.

Afterward, however, PennDOT said traffic may be stopped intermittently for 15 to 30 minutes at a time throughout the day tomorrow and Sunday.

The traffic stoppages will be implemented as a precautionary measure while workers use two dozen heavy-duty hydraulic jacks to adjust and reposition the 150-foot-long southbound span that came loose and dropped about 8 inches in the middle of the night of Feb. 8.

The 2.1 million-pound span crashed onto Pier No. 10, a land pier located between Second Avenue and the Monongahela River.

Since the incident, reported by an unidentified motorist, the six-lane bridge has been closed. By lifting and setting the span entirely on a newly built temporary support system, PennDOT hopes to reopen the bridge by Monday to one lane of traffic in both directions.

The span is currently resting on both the temporary support system and Pier 10.

"We don't know what the shifted pier will do once the weight is taken off it of it," PennDOT District 11 spokesman Jim Struzzi said.

PennDOT has hired an engineering firm to investigate the cause of the bridge problem, believed to be due in whole or part to "frozen" rocker bearings that enable the bridge to expand, contract and otherwise "flex" under different traffic loads. PennDOT has confirmed that the bearings had advance rust and corrosion that led to their malfunction. The rocker bearings have been replaced with a temporary, different type of bearing system.

The northbound side of the bridge will remain closed while those rocker bearings are replaced on the parallel span in order to minimize chances of a recurrence. Then, PennDOT will determine whether the 50-foot-tall southbound pier can be shored up or whether it will have to be replaced.

The Birmingham Bridge was opened in 1976 and carries nearly 23,000 vehicles a day. It is 2,747 feet long and consists of 19 spans in total, including the one that dislodged and dropped. The bridge was last inspected in 2006, when engineers found no reason to classify the bridge as structurally deficient and the rust on rocker bearings was considered to be "moderate."

Tomorrow morning, the Parkway East closure will be between Grant Street (Exit 1) and Bates Street (Exit 3) in both directions.

Generally, westbound traffic will be detoured at Wilkinsburg, including Swissvale and Squirrel Hill traffic that will be sent outbound to get off at Wilkinsburg and circle back. Then drivers will be detoured onto Fifth Avenue to Downtown to re-enter the parkway westbound at Grant Street.

Eastbound traffic from the Parkway West/I-279 will be sent to Route 28 north to the Highland Park Bridge to Route 8 south to Route 130 to the Parkway East or to Route 28 to Route 910 to Freeport Road to the Pennsylvania Turnpike to Monroeville.

Eastbound traffic from I-279 south and from Routes 65, 51 and 19 will be sent through the Liberty Tunnels to I-579 north to Bigelow Bouelvard to Baum Boulevard to Penn Avenue to Route 8 south to return to the Parkway East.