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[4:40 p.m. update: Metrobus has issued several alerts about afternoon changes on the S Line because of traffic congested anticipated around 16th and M streets NW. The S9 begins service at 11th & I (Eye) streets. The S2 and S4 detour on P Street between 13th and 16th streets. The 42 detours on 13th Street. A9 buses begin service at 13th and H streets. Westbound 32/34/36 buses detour via Constitution Avenue between 15th and 23rd streets. Eastbound 32/34/36 buses detour via Constitution Avenue between 10th and 19th streets. The 80 detours on Constitution Avenue between 12th and 19th streets NW. The 16Y is departing from a temporary bus terminal at 19th and H streets NW.]

Commuters who travel north and west from downtown D.C. may want to consider making this an early day, so they don’t have to make it a late one.

President Obama is scheduled to attend a Democratic National Committee event at the Jefferson Hotel, 16th and M streets NW, shortly after 5 p.m. Tuesday. If he sticks to that schedule, many drivers and bus riders won’t be able to stick to theirs.

Commuters who travel north-south on 16th Street or west on M Street toward Georgetown and the Key Bridge are likely to be hard hit by even a temporary street blockage near the hotel, but recent history shows that the effects extend for many downtown blocks.

Metro is warning riders who take the S-Line buses on 16th Street (S1, S2, S4 and S9) to expect delays during the afternoon commute. Metro spokesman Dan Stessel offered a tip that could work for some transit riders: Take Metrorail’s Green Line to Columbia Heights, exit to Irving Street and walk one block west to 16th Street, then catch a bus there.

Residual impacts will be felt on all bus lines using K, I and H streets, Stessel said. “We expect bail out traffic will likely tie up 14th Street, Connecticut and Massachusetts.”

Aside from the S-Line, he said, other routes likely to be affected are the 3Y, 11Y, 16Y, 32, 36, 80, D6, P17, P19 and W13.

Bus riders should watch for Metro alerts via e-mail and text and by Twitter. They will announce detours as they are established by street-level supervisors, Stessel said. It is possible that S-Line buses will get shifted over to 14th Street below Massachusetts Avenue, though that decision will be made if or when 16th Street is closed or becomes gridlocked. “Anyone who has the option of using Metrorail to get out of downtown should consider that as an alternate tonight,” Stessel said.

Metro did not have advance word about the presidential visit, the same type of situation that led to a scramble by Metrobus officials Feb. 20 when an event at the St. Regis Ritz hotel at 16th and K streets NW jammed afternoon traffic.

Pedro Ribeiro, chief spokesman for D.C. Mayor Vincent C. Gray (D) told Post reporter Peter Hermann Tuesday that District officials are aware of the president’s afternoon visit, but Ribeiro said they are not concerned about such short visits. “Those we can handle,” he said.

Gray had criticized the U.S. Secret Service earlier this month after a prolonged closure of 14th Street Northwest between Pennsylvania Avenue and G Street, when Israeli Prime Minister Benjamin Netanyahu stayed the Willard Hotel for a conference. The Secret Service had that road shut down for three days, snarling rush-hour traffic.

Gray complained that the District got little notice of the closure and the Secret Service promised to work more closely with local officials. Gray even asked that dignitaries be put up in hotels away from downtown if their presence requires such an imposing security clampdown.

Ribeiro said that brief visits such as the one Tuesday afternoon result in street closures. He said that Paul A. Quander Jr., the D.C. deputy for public safety and justice, is scheduled to meet with the Secret Service on this issue next week.

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