WASHINGTON, March 15 - The second-biggest U.S. subway system, which serves Washington D.C., will close for 29 hours at midnight EDT (0400 GMT) on Tuesday for emergency safety checks, leaving hundreds of thousands of government workers, tourists and business travelers struggling to get around town.

Transit officials in the nation's capital announced the unprecedented closure of the Washington D.C.-area Metro subway system so it could inspect 600 underground cables after a cable fire this week caused delays. The subway will reopen at 5 a.m. EDT (0900 GMT) on Thursday.

The Office of Personnel Management, which oversees the federal workforce, said government offices would remain open but federal workers could take unscheduled leave or work from home. Congress will be open.

Ed Etzkorn, a 43-year-old federal employee, said he had no idea how he and his wife, also a government worker, would get to work.

"We're going to have to figure that out tonight," he said. "It's awkward for those of us who have to commute, but I understand they need to do what they need to do for our safety."

About 700,000 people ride Metro on average every week day including about a third of the region's federal workforce.

The area has some of the worst traffic in the United States, and local radio station WTOP predicted the subway closure would cause "major mayhem" on the roads.

Meissa Toure, who rides Metro twice a week, said Wednesday would find him behind the wheel of a car. "I'll definitely be driving tomorrow. It's going to be a mess tomorrow. I plan to leave about 30 minutes early."

Buses will run normally on Wednesday, and parking will be free in Metro-owned lots and garages, the transit agency said.

Metro riders said they welcomed the shutdown as an indication that Metro was getting serious about safety even though it would snarl their commutes.

"We don't have any way to commute. I live way out, so the subway is the only way to get in," said Regina Smith, 50, a federal worker from Quantico, Virginia. She hoped she could telecommute.

Tourist Holly Morris, 57, a teacher from Shorewood, Wisconsin, in town with her family, said she had not heard about the shutdown. "That's difficult for us to get around in an economic fashion. We'll have to use taxis, buses, but we don't have bus cards, so that's stressful."

San Francisco-based ridesharing company Lyft said it was expecting high demand and offered new customers $20 off their first ride.

Uber said it would cap surge pricing in the Washington area at 3.9 times base fares during the shutdown. It said it was expanding uberPool coverage across Washington, Maryland and the Virginia metro area.

The closure of the 119-mile (230-km) subway system, which has been plagued by equipment breakdowns and fires, will allow safety officials to inspect the cables for worn-out casings, Washington Metropolitan Area Transit Authority General Manager Paul Wiedefeld said at a news conference.

"While the risk to the public is very low, I cannot rule out a potential life safety issue, and this is why we must take this action immediately," he said.

Wiedefeld said the shutdown was prompted by a cable fire on Monday that caused delays on three of the system's six lines.

Cherry blossom time

Washington is a major tourist destination all year but attracts more visitors in spring when cherry trees blossom around major landmarks like the Jefferson Memorial.

Many of its hotels, which cater to business people and tourists, were sold out last week, making last-minute bookings by commuters difficult.

In Takoma Park, a Maryland suburb near Washington, residents quickly resorted to a neighborhood listserv to organize carpools. Capital Bikeshare, which allows people to rent bicycles for hours at a time, was offering free 24-hour memberships on Wednesday.

Matt Keller, who lives in Maryland and works at the Liechtenstein embassy, said, "I decided to bike it in and see how it goes. Busing will have its own challenges, and the streets will probably be pretty clogged."

Wiedefeld said the closure was the first shutdown of Metrorail that was not weather related since operations began in the 1970s.

The shutdown underscores safety concerns that have plagued Metrorail for decades.

Safety supervision of Metrorail was placed under the Federal Transit Administration in October. It was the first time a U.S. subway system had been put under direct federal oversight for safety lapses.

Since the 1980s, the National Transportation Safety Board has conducted 11 investigations into Metro accidents that have killed a total of 18 people.

Under the vaulted ceiling of the main downtown Metro station, lighted red signs warned of the imminent shutdown.

"Safety first, but, I mean, it's a mess," said Theresa Spinner, a public relations specialist. "I have a job interview tomorrow morning, and I already have reserved a cab," she said.

Absences at public schools will be excused and some charter schools may close, officials said.