New York City transit riders steamed with anger in stalled subway cars during the peak of the Friday evening rush hour when a computer network lost communications with the signal system, which directs rail traffic.
Subway lines 1, 2, 3, 4, 5 and 6 as well as the S shuttle between Grand Central Terminal and Times Square were suspended in both directions just before 6 p.m., stranding cars in tunnels and leaving riders in a crush on platforms and steps during the heat wave.
Transit officials rebooted the computers, and the system gradually came back online just after 7:30 p.m., officials said.
As city officials railed against the MTA, NYC Transit president Andy Byford, at an 8:30 p.m. news conference, ordered an investigation into what led to the computer failure at the Rail Control Center in Manhattan and why the backup system did not kick in.
Before the system came back online, Mayor Bill de Blasio harshly criticized the MTA and dispatched the city's emergency management team to assist. Without any idea where their subway trains were, MTA workers had to determine where each was and what was ahead of them before directing certain trains back to platforms, allowing passengers to get off, Byford said.
Byford, at the news conference, said he did not know the root cause of the problem.
"My priority was to make sure that people are safe and to get them moving," he said. "We will get to the bottom of this. What we know is for reasons yet to be identified, we lost indications on the signals so that our Rail Control Center could not see where the trains were on the numbered lines. Obviously, you've got to know where trains are in order to be able to move them."
He said he understood the frustration of riders, many of whom tweeted their anger while trapped in cars.
"What should we use as a bathroom now that we live down here?" Douglas Smith Land tweeted about 7 p.m.
NYCT Subway responded, "As a fellow PennPlanner, I urge you to please hold it. We're working to get everyone moving as quickly as we can. Thanks."
That got Stephanie Turner tweeting back in capitals: "THIS IS NOT OKAY. You need to fix it fast! People are overheated and getting sick."
The mayor chimed in on Twitter also: "This kind of meltdown during a heat wave is UNACCEPTABLE," he typed. "The MTA owes every single New Yorker an explanation for this. We've known about this dangerous weather for DAYS. There’s no excuse for why they aren't prepared."
MTA officials had urged riders to remain in their rail cars, and the subway system was handing out courtesy passes and advising riders to take lettered subway trains and buses.
At the World Trade Center No. 1 line station during the disruption, a clerk issued refund tickets and directed people to other nearby lines.
Passengers — many of them visitors to New York — seemed to take it stride.
"It's about what I expected," said Derek Lloyd, who's from Hanover, Massachusetts, near Boston and its transit system. "I don't know that ours is much better," he said with a smile.
On one line that was running, passengers packed into one car that didn't appear to have air conditioning. Sweat glistened on riders' skin as they sought relief, fanning themselves and one another.
As they waited for service to be restored, riders criticized a lack of updates and other problems they say they've endured for too long.
"Not to be dramatic but I wish the absolute worst for every mta employee right now," Fran Fine Stan Account wrote on Twitter.
NYCT Subway replied, "But then how will we fix the trains?"