[This post has been updated]

5:35 p.m. Update: Metro’s chief spokesman Dan Stessel said the transit authority has identified the cause of the outage as the failure of a UPS, an “uninterruptible power supply.” Engineers are investigating why the UPS failed, he said.

“To prevent a recurrence in the near term, we have placed the UPS in a ‘bypass’ mode,” Stessel said, “and will assign a power technician to provide around-the-clock monitoring of the UPS until a permanent fix is made.”

Original post: Metro is investigating a power outage that left riders stranded on station platforms and stuck in train cars late Thursday night into Friday, without any communication from transit officials.

The outage occurred shortly before midnight, Metro officials said. As a safety precaution, trains on the Red, Orange and Blue lines were held in stations from about 11:55 p.m. until 12:10 a.m.

However, reports on Twitter about possible problems began surfacing 30 minutes earlier.

The outage coincided with scheduled track work on the Red, Orange and Blue lines.

Metro had previously recommended that riders add up to 25 minutes to their travel times Thursday night, meaning the outage resulted in “significant delays,” according to the transit agency.

The outage occurred hours after a broken rail caused major delays and a chaotic morning commute on the Red Line. Earlier Thursday, Metro’s board of directors voted to hold public hearings to discuss proposed fare increases.

Officials said that the partial outage affected computer systems and radio consoles at bus and train control centers, as well as the transit agency’s communications systems and the WMATA Web site.

As a result, stranded passengers did not receive information about why or for how long they would have to wait.

Metro reports that all systems are now operating normally and should not affect Friday’s morning commute.

The cause of the power outage is unknown and remains under investigation, officials said.

Were you among the passengers affected by overnight Metro delays? Tell us in the comments.