Emergency personnel stand outside the Tenleytown-AU Metro station as people emerge while it was shut down due to a Red Line train being stuck in a tunnel on Wednesday. (Photo by Matt McClain for The Washington Post) (Matt McClain/FOR THE WASHINGTON POST)

A pair of power failures on opposite sides of Metro’s Red Line created a mass-transit mess Wednesday morning, leading to single-tracking, severe overcrowding, a train evacuation and at least two hospitalizations.

Thousands of commuters were stranded on platforms and on the rails, and dozens of riders had to be evacuated from a stranded train because of the breakdowns, which began toward the end of the morning rush.

The stations most affected were NoMa-Gallaudet U, Rhode Island Avenue-Brentwood, Van Ness-UDC, Tenleytown and Friendship Heights, but there were serious delays throughout the Red Line.

The trouble began about 8 a.m. when a power problem near the Rhode Island Avenue-Brentwood station halted a train heading to Glenmont. Trains began single-tracking between Rhode Island Avenue-Brentwood and NoMa-Gallaudet U as emergency crews responded to the stalled train.

Just as 60 or so passengers from that train were boarding shuttle buses to Rhode Island Avenue, a similar power problem occurred about 9 a.m. on the Red Line between Friendship Heights and Tenleytown. An eight-car train carrying about 1,000 passengers toward downtown became stuck near the Tenleytown-AU station.

“All of a sudden, the lights went out, the AC went off,” said Alcora Walden, a Germantown resident who was commuting from Shady Grove to Metro Center. “It got really quiet. It felt like we were rolling, like it was momentum carrying us and not the train. Then we came to an abrupt stop.”

Metro said it is trying to determine what led to the power failures.

After the problems began, Metro issued warnings of delays, urging commuters to avoid the Red Line — the transit agency’s busiest rail line — and to consider using the Green Line or Metrobus instead.

But for Walden and many other passengers already on trains without cellphone service, waiting in stations or unable to hear garbled announcements from train operators, it was too late.

As the morning progressed, the delays mounted. Riders at various stations, from Fort Totten to Union Station to Friendship Heights, began posting photos and complaints on Twitter.

“I’m looking at a 2-hour commute! Shout out to the erratic (yet I remain faithful) Red Line. Talk about a great way to kick [off] my day,” tweeted rider Keyon Smith.

Other riders abandoned public transportation altogether. “I’m not the only one hoofing it. We’ve got [an] ex-red line riding convoy here walking to points east,” commuter Steven Schwark tweeted.

Two of the riders from the train stuck near Rhode Island Avenue were taken to a hospital as a precaution, according to Battalion Chief Brian Lee, a D.C. Fire and EMS spokesman. A few other passengers were evaluated at the scene, and the rest were transferred to shuttle buses and taken to the Rhode Island Avenue-Brentwood stop.

The passengers who were stuck near Tenleytown were stranded for nearly an hour as Metro officials and emergency crews weighed whether to evacuate the passengers through the tunnel.

Metro crews dispatched to check on the power got stuck in traffic, adding to the delays.

Vasanth Sridharan, a paralegal commuting from Rockville to Metro Center, said the train was stopping frequently before it stalled near Tenleytown.

“At one point, they said they were going to evacuate, but then they told us not to leave because they didn’t know if the third rail was live,” said Sridharan, 27. Then the power came back on, and the train continued on its way.

“Anyone who rides Metro every day is going to have delays every now and then, but this was a little different,” he said.

Police officers walked through the tunnels and checked on passengers to see whether anyone needed medical assistance.

Walden, who normally takes a MARC train, chose Metro on Wednesday because of severe delays on MARC’s Brunswick Line. She was ready to be on her way. She stuffed all her belongings into her backpack, tied her shoelaces “extra tight,”and pulled out the flashlight and pocketknife she carries with her.

But before anyone stepped into the narrow tunnel, the lights began to flicker, followed by a blast from the air conditioning and what Walden described as “a herky-jerky start.”

Power was restored to the train shortly after 10 a.m., and the train moved to the Tenleytown station. According to Metro Transit Police Deputy Chief Leslie Campbell, about 20 to 30 people chose to get off the train at that point, including a woman who Campbell said became ill. She was taken to Georgetown Hospital for evaluation.

Walden, still several miles from her destination, chose to get off the train. She said there was confusion at Tenleytown, where nearby streets had been closed and traffic was a mess. She walked part of the way before catching a cab downtown.

Delays persisted after the second train moved, with trains running at reduced speeds of 35 mph as a precaution. The Red Line resumed normal speeds by 12:30 p.m.

Peter Hermann and Luz Lazo contributed to this report.