Like the wheels on the bus, transit commuters will be going round and round trying to get Downtown during the G-20 summit.

The Port Authority yesterday released detours for dozens of bus routes affected by Downtown road closures.

"Every route that goes Downtown will be affected during the G-20," said Port Authority spokesman Jim Ritchie.

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Though many routes will simply be tweaked as they enter and leave the Golden Triangle, other routes will be detoured significantly.

Buses that use the East Busway, for example, will be routed through Oakland onto Centre Avenue, which they will follow through the Hill District to Fifth Avenue into Downtown.

Buses that usually enter Downtown through the Strip District will get as far as 26th Street on Liberty Avenue, then backtrack to Oakland, where they will also pick up Centre Avenue.

And some buses that normally take the Parkway East to Downtown will detour to Second Avenue and then to Carson Street on the South Side, making their way into the Golden Triangle on the Smithfield Street Bridge.

It's impossible to estimate how much longer than normal some of those routes might take, said Mr. Ritchie.

"We're hoping for the best but we really do know that some of these routes, it's really going to add some time onto the trip," he said.

Given the numerous road closures announced yesterday by the city -- and narrow city streets that make planning detours difficult -- the circuitous routes couldn't be avoided, said Mr. Ritchie.

"It's either that or we don't run the buses."

Once the buses enter Downtown, most routes will be funneled into the Boulevard of the Allies corridor, he said.

Buses will be using one of four main access points into Downtown, said Mr. Ritchie: The Clemente Bridge; I-279 HOV lanes from the Veterans Bridge; Smithfield Street Bridge or Fifth Avenue. The T light rail service will run as far as First Avenue, but other Downtown stations will be closed.

To help riders figure out where to catch their bus on the reconfigured routes, Port Authority workers will staff Downtown streets and offer directions, he said. The Port Authority will also be communicating route information before and during the event via its Web site, e-mail and Twitter.

Depending on events during the summit, routes might need to be tweaked further.