The second phase of road and bridge reconstruction at the gateway to Oakland will create major obstacles for motorists starting next month.

The traffic challenges will start at midnight Jan. 3, when the Boulevard of the Allies outbound approaching Oakland will be closed for 11 months, as will the exit ramp that touches down on Forbes Avenue.

Over the weekends of Jan. 4-6, Jan 18-20 and Feb. 1-3, Forbes Avenue is to be closed as well, sending traffic to Second Avenue and Bates Street or out the Parkway East/Interstate 376 to the Swissvale-Edgewood interchange, where drivers can circle back to Oakland.

During those periods, two deteriorated Boulevard of the Allies bridges will be razed, including the bigger boulevard bridge, which will be dropped directly onto a 4-foot-thick cushion of dirt, steel plates and wooden timbers on Forbes designed to protect underground utilities.

Forbes will remain open over the two January weekends when the University of Pittsburgh's basketball teams will be playing home games.

The myriad of traffic restrictions and detours for the second season of the $29 million bridge and interchange reconstruction project were outlined yesterday by the Pennsylvania Department of Transportation and its contractor at a meeting in Pitt's Alumni Hall.

While the project to create a modern Oakland gateway will improve traffic flow, "people will have to endure some dramatic changes in the meantime," PennDOT District 11 Executive Dan Cessna said. "We made lots of progress" this year, when a ramp was built to provide a direct connection from Fifth Avenue to the Boulevard of the Allies inbound, he said, "but work on the big prize has yet to begin."

While the boulevard outbound will be closed beyond the Birmingham Bridge and the ramp to the Parkway East, the traffic impacts will extend far beyond South Oakland, starting Jan. 3. For example:

• Motorists headed toward Pittsburgh on Route 28 or Interstate 279 will be unable to get to Oakland using the Veterans Memorial Bridge and the Crosstown Boulevard/I-579. They'll be directed to the Fort Duquesne Bridge and Parkway East outbound to the Oakland/Forbes Avenue exit.

• Motorists crossing the Liberty Bridge will be unable to take the ramp leading to the boulevard and Oakland. They'll have the option of using Grant Street to the Parkway East or taking Forbes Avenue past Duquesne University, Mercy Hospital and Uptown.

• Downtown traffic destined for Oakland also will have to use the Parkway East or follow Forbes Avenue over the entire two miles.

Almost as soon as Pitt and Carnegie Mellon University dismiss classes for the 2007-08 academic year in the spring, PennDOT will funnel traffic on Forbes into one lane through the work zone for about two months.

During the upcoming phase of construction, the city will close the Forbes Avenue ramp leading to the Boulevard of Allies via a jog over residential streets and Craft Avenue.

"We encourage people to make trial runs over the detour before Jan. 3 or figure out alternative routes," advised Jim Foringer, PennDOT's assistant district executive for construction. "There are lots of back ways in and out of Oakland."

Oakland-bound drivers who head out the Boulevard of the Allies by mistake will encounter a "contingency detour" that sends them out the Parkway East through the Squirrel Hill Tunnel to the Edgewood-Swissvale interchange and then back again via the Parkway East inbound.

The two new bridges, rebuilt boulevard and new ramps are to be opened by late November. Landscaping, paving and minor work are to be completed during nonpeak hours in spring 2009.

PennDOT plans to take advantage of traffic being diverted from the boulevard to do other work next year, including repaving the inbound lanes from South Oakland to Downtown and repaving the Crosstown Boulevard/I-579 and ramps below Mellon Arena.

In addition, PennDOT will continue the rehabilitation it has been doing for the past two years on the Parkway East, starting in 2008 at the Edgewood-Swissvale interchange and extending east to Churchill.