Metro announced that its entire rail system would cease operations for 24 hours so crews can inspect cables throughout the system. Here are how some riders feel about the shutdown. (Lee Powell/The Washington Post)

Metro announced that its entire rail system would cease operations for 24 hours so crews can inspect cables throughout the system. Here are how some riders feel about the shutdown. (Lee Powell/The Washington Post)

(Latest: Washington braces for full day of Metro shutdown to deal with safety concerns)

The entire Metrorail system shut down at midnight Tuesday for at least a full day in an unprecedented move by transit officials, who said they acted because they feared for the safety of passengers of the nation’s second-busiest subway system.

The new general manager, Paul J. Wiedefeld, and the Metro board decided to suspend operations all day Wednesday to conduct emergency inspections of electric cables, raising new alarms about the beleaguered 40-year-old rail system’s ability to deliver safe, reliable service.

The paralysis of the core of Washington’s transportation network, announced Tuesday afternoon just half a day before it was to take effect, sent a shudder through the region and sparked angry complaints about Metro’s inadequacies. Hundreds of thousands of commuters, schoolchildren and others made new plans to get around Wednesday.

But Wiedefeld said that it was too risky to delay the safety checks after an electrical fire erupted early Monday and poured smoke into a Metro tunnel downtown.

1 of 45 Full Screen Autoplay Close Skip Ad × Images from the smoke-filled train and rescues at L’Enfant Plaza station in 2015 View Photos One person died in the January 2015 Metro incident in a tunnel outside the L’Enfant Plaza Metro station after scores of riders were trapped aboard a train as it filled with smoke. Caption One person died in the January 2015 Metro incident in a tunnel outside the L’Enfant Plaza Metro station after scores of riders were trapped aboard a train as it filled with smoke. Jan. 12, 2015 Passengers react Monday afternoon as smoke fills a Metro train in a tunnel outside L’Enfant Plaza Metro station. Saleh Damiger Buy Photo Wait 1 second to continue.

The incident, caused by malfunctioning electric cables, was eerily reminiscent of the fatal Yellow Line smoke incident 14 months ago that resulted in the death of one passenger and sent scores to the hospital.

] Metro delays caused by cable problem similar to last year’s fatal smoke incident]

“While the risk to the public is very low, I cannot rule out a potential life-safety issue here, and that is why we must take this action immediately,” said ­Wiedefeld, who started in November. “When I say safety is our highest priority, I mean it. That sometimes means making tough, unpopular decisions, and this is one of those, for sure. I fully recognize the hardship this will cause.”

Metrorail has closed because of bad weather — including during January’s blizzard — but never for safety reasons. During the shutdown, crews will inspect all 600 of a type of power line, called “jumper cables,” in tunnels throughout the system to ensure that they are sufficiently insulated and are otherwise reliable.

The hope is that no problems will be found in the inspections so the system can reopen at 5 a.m. Thursday. But if problems are identified, individual Metro lines or stations could remain closed Thursday and beyond.

The surprise announcement sent the federal government and local school districts scrambling to adjust.

The Office of Personnel Management granted all federal agencies in the region the option to allow employees to take unscheduled leave or telework.

The entire Metro system is shutting down for at least 24 hours on Wednesday, March 16, impacting thousands of commuters. (Alice Li/The Washington Post)

No school systems closed because of the shutdown, but some officials expressed concern over how teachers and other employees might get to work.

At schools in the District, all tardies and absences will automatically count as excused. Because a good portion of D.C. students do not attend a neighborhood school, they rely on Metro to commute. Some charter schools also announced closures.

[LIVE updates on what will happen when the system shuts down]

The shutdown does not affect Metrobus service. But transportation systems that feed into Metrorail, including the Fairfax Connector bus service, were considering adjustments in service Wednesday.

The shutdown acted almost as an exclamation point after years of deterioration, mismanagement and safety lapses that have tarnished a subway system that once was an emblem of efficiency and source of regional pride.

Still, longtime critics of Metro’s shortcomings generally defended the decision on the grounds that riders’ safety was the top concern.

Metro “has a long, well-documented list of safety issues and needs to work aggressively to fix them,” U.S. Transportation Secretary Anthony Foxx said. “While this shutdown is inconvenient, they are doing the right thing by putting the safety of their passengers and workers first.”

Foxx also used the occasion to urge the District, Maryland and Virginia to step up their efforts to exert safety oversight of Metro. In October, Foxx gave the Federal Transit Administration responsibility for safety oversight of the rail system. He said the body previously in charge of it, the Tri-State Oversight Committee, composed of representatives of the three jurisdictions, had failed to do its job.

The three jurisdictions have agreed to set up a more powerful body, to be called a Metro Safety Commission. But that process has been delayed by as much as a year because neither Virginia nor Maryland moved to obtain necessary approval from their general assemblies during this year’s legislative sessions.

“I’ve said it before,” Foxx said, “and I’ll keep saying it until the region takes real ownership of its safety-oversight responsibilities: D.C., Maryland and Virginia need to stand up a permanent Metro safety office with real teeth.

“What are folks waiting for?”

Sen. Barbara A. Mikulski (D-Md.) called the decision “an incredible disruption to everyone who uses Metrorail” but added, “ ‘Safety first’ must be a mandate.”

D.C. Mayor Muriel E. Bowser (D) said she was not privy to the information that led Metro leaders to close the rail system and wouldn’t second-guess the decision until she knew more. But she said that eventually, she wants to know how Metro arrived at the point of needing a sudden and complete shutdown.

“Do we want to understand their decision-making to get to this point? Of course, and we will get to those answers,” Bowser said. “Some of the questions I will have have to do with what options did they look at to do this? Is a 24-hour or 29-hour closure the only option?”

The shutdown was decided in an hour-long conference call starting at 2 p.m. with most Metro board members, during which Wiedefeld recommended the immediate, one-day shutdown as the best option, officials said.

Board members raised concerns and discussed other possibilities but ended up endorsing the general manager’s view with little dissent.

The safety checks could have been delayed until the weekend or conducted at night over about six days, officials said. But if the system were kept open, a public announcement about the risk would have to be made. That would have put passengers, and Metro, in the awkward position of publicly acknowledging that it was operating despite being aware of a potentially deadly safety problem.

Metro also would have been liable in the case of any crashes or calamities.

Metro officials offered no new details about the location or seriousness of Monday’s early-morning tunnel fire that snarled service on the Blue, Orange and Silver lines.

“The investigation into yesterday’s cable fire at McPherson Square is ongoing,” Wiedefeld said. “As a preliminary matter, the conditions appear disturbingly similar to those in the L’Enfant incident of a year ago, and our focus is squarely on mitigating any risk of a fire elsewhere on the system.”

The cable fires have “happened twice in a year,” Wiedefeld said, adding that he couldn’t risk “a third time.”

In an especially unnerving revelation, Wiedefeld confirmed that the cable that caught fire Monday had been inspected as part of a systemwide cable inspection after the Yellow Line fire — and passed. He said he had concerns about the results of that inspection.

Wiedefeld said 125 cables were replaced after the inspections.

A Metro official who spoke on the condition that he not be identified because he was not authorized to speak publicly said the earlier cable inspections were not conducted properly or missed the problem that caused the fires.

[What happened on Monday and the havoc it caused]

Pressure has been growing for fixes to myriad problems that have plagued Metro since the January 2015 incident. That fatal calamity came six years after Metro pledged to put safety first following a deadly 2009 Red Line crash that killed nine people, including a train operator. It only raised concerns that the system had made little progress.

A series of other service breakdowns, including an August derailment on a stretch of track that Metro officials knew for a month was problematic, as well as other management failures further raised questions about the agency’s ability to provide safe, reliable service.

Even as many riders have turned away from the Metro system, blaming almost weekly service disruptions, many thousands still depend on it to get to work. And with Wednesday’s shutdown, they will be confronted with the unimaginable.

“Tomorrow we will get a glimpse of what our nation’s capital will look like without this essential system,” said Rep. Don Beyer (D-Va).

Other members of the region’s congressional delegation were also frustrated by the news.

“Today’s decision by General Manager Wiedefeld to shut down the Metrorail system for 24 hours is a gut punch to the hundreds of thousands of commuters who depend on the system,” said Rep. Gerry E. Connolly (D-Va.). “While I am extremely frustrated with this news, safety must be our number one priority. This dramatic action highlights the need for long-term safety and reliability improvements throughout the system.”

[Tracking Metro’s biggest meltdowns]

D.C. Council member Mary M. Cheh (D-Ward 3), head of the council’s transportation committee, said she received no official warning and learned of the news from the Internet when it leaked before the official announcement.

“The problem sounds mysterious, and maybe this is a fairly dramatic step, but maybe it’s the kind of step that we need to get things right,” Cheh said. “I told the people in my office, ‘Break out your bikes.’ ”

The Metro board’s chairman, Jack Evans, who took the post in January, supported Wiedefeld’s action.

“The most prudent thing is to close down the system and find out what we’re dealing with,” said Evans, who also is a D.C. Council member. “I am not willing to take a chance.”