Pope Francis greets a couple and their child in St. Peter’s Square on Sept. 9, 2015. Francis’s first visit to the United States as pope begins Sept. 22. (Osservatore Romano Press Office/European Pressphoto Agency)

The pope’s historic visit to Washington later this month prompted federal security officials and Mayor Muriel E. Bowser on Thursday to offer a strong word of advice to residents and workday visitors alike: If you can, work from home the week after next. And if you must, really must, go downtown, take only public transportation.

Some major roadways, including northbound Massachusetts Avenue, will be closed for three days around the first visit to the United States by Pope Francis. An open-air Mass will send tens of thousands flooding into an area around Catholic University, with no way for the crowds to disperse quickly. And a popemobile parade around the Ellipse as well as Jumbotrons set up for public viewing of the parade will make parts of the Mall all but impassable over parts of two days.

“We want to have a lot of activity downtown, but on the traffic side, if you have to use a vehicle . . . you will really need to plan ahead,” said Leif Dormsjo, the District’s director of transportation. “These road closures will be long in duration and they will impact some significant arterial streets.”

With the District weeks behind New York and Philadelphia in announcing details of its leg of the pope’s U.S. visit, Bowser (D) and James M. Murray, the special agent in charge of coordinating the visit for the U.S. Secret Service, confidently predicted that with help from residents, Washington will be ready for crowds of whatever size that descend on the nation’s capital starting Sept. 22.

To prepare, Bowser urged private employers to allow their workers to telecommute during the visit, as federal employees have been told to do, as if a September snowstorm has paralyzed the region.

The recommendation on working from home left Bowser walking a fine line with city business leaders. After holding a news conference on the papal visit, Bowser and Murray met privately with hundreds of store owners, and the mayor assured them that the District will remain “open for business,” according to attendees.

More than anything, Thursday’s security briefing on the pope’s visit offered the first detailed guidance for how to get as close as possible to the papal action — or, if you prefer, how to stay away.

On the afternoon of Sept. 22, a Tuesday, Francis will arrive at Joint Base Andrews in Maryland and travel to the Vatican Embassy — formally known as the Apostolic Nunciature of the Holy See in the United States — on Massachusetts Avenue near the Naval Observatory compound, where the vice president lives.

The masses expected to line Massachusetts Avenue to celebrate the arrival could be among the first to glimpse the pope in the United States.

The rush-hour scene near the Vatican Embassy, where Francis will stay, will also hint at the spectacle to follow: For three days, not a single private vehicle will be allowed to travel out of Washington along northern Massachusetts Avenue, one of the busiest roads in the nation’s capital.

To maintain a secure perimeter around the pope, northbound Massachusetts Avenue will be shut down for blocks in either direction for the duration of his stay. Rolling roadblocks will also shut down southbound lanes when he is arriving at or leaving the embassy.

On Sept. 23, the pope will visit the White House, forcing staggered road closures downtown. After Francis meets with the president, a papal parade is expected to draw the largest crowd for any non-ticketed event.

See details on each of the events in the Pope’s visit

Francis will ride in the popemobile, a customized Jeep Wrangler with a glass enclosure, around the Ellipse, south of the White House, starting about 11 a.m.

Not even the earliest commuters will escape the disruption. Security screening areas for the parade will open at 4 a.m. and the Mall is expected to fill near the Washington Monument where people will watch video feeds from the White House and events later that day on a Jumbotron.

Among the events will be a Mass, which the pope will deliver in Spanish, his native language, outside the Basilica of the National Shrine of the Immaculate Conception at Catholic University.

That event is expected to draw at least 25,000 people to a corner of the city that rarely sees such a crowd and where road closures could detour as many as 70 bus routes, officials said.

Only one Metro stop, Brookland, is near the basilica.

Jack Requa, Metro’s interim general manager, dryly predicted long wait times. “There will be delays,” he said Thursday when asked about Metro’s planning for the papal visit.

Requa said the troubled subway system would largely run on regular, morning rush-hour service. He said any additional trains possible would be put into service to alleviate congestion around the pope’s events.

On Sept. 24, the city will take on the air of an inaugural, with Constitution and Independence avenues shut down when the pope addresses a joint meeting of Congress, and possibly greets visitors outside the U.S. Capitol.

He also plans to visit a Catholic charity feeding the homeless downtown before departing for New York.

Murray, the Secret Service special agent, said the pope’s visit would be the 50th event designated a national special security event in the past 20 years, a classification that draws in hundreds of federal law enforcement officers, the National Guard and other government resources.

Murray declined to give specific examples of security planning but said 23 teams have met on separate issues. Those include airspace security and crowd management. The crowd management challenge involves not only accommodating those entering, he said, but in the case of something going awry, also aiding tens of thousands in quickly exiting an area.

Citing several illegal landings by drones and an ultralight on federal land in the District in the past year, Murray bluntly warned against the flying of drones to get better views of the pope.

Bowser, a Catholic, said she was thrilled to welcome “the pope, my pope,” to Washington, and she predicted that the city would have a successful visit. “We know a thing or two about” hosting major events, she said.