DC Metro train derailed 3 times on the same day before passengers were forced to evacuate through a dark tunnel, investigators say

• A train on the Washington, DC, Metro's Blue Line derailed last week, causing passengers to exit through a tunnel.
• The train derailed at least two other times in the dame day, NTSB investigators said Monday.

The train on the Washington, DC, Metro system's Blue Line that derailed with passengers aboard last week had derailed at least two other times earlier in the day, investigators with the National Transportation Safety Board said Monday.

The NTSB said at a news conference Monday investigators determined that derailment of the 7000-series train was the result of its wheels shifting too far apart on their axles. A preliminary investigation said similar wheel problems existed on certain Metro trains since 2017, the agency said at a news conference Monday, according to DCist.

"We are fortunate that no fatalities or serious injuries occurred as a result of any of these derailments, but the potential for fatalities and serious injuries, was significant," said NTSB Chair Jennifer Homeny at the agency's DC headquarters.

"This could have resulted in a catastrophic event," she added.

Metro had previously reported 31 wheel assembly failures on the 7000-series trains since 2017, the NTSB said Monday, per DCist. Following the derailment, another 21 cars that were inspected were found to have the same issue. Prior to the conference Monday, investigators had inspected 514 of the 748 7000-series cars and said they could find additional trains with the issue, the report said.

According to NTSB investigators, the same train had at least two other derailments and re-ailments the same day prior to the derailment outside the Arlington Cemetery station on the Blue Line. Investigators found pieces of the train's brake discs at its Largo and Rosslyn stations. The pieces broke from the train during the previous derailments, investigators believe.

The first two derailments occurred around 3:20 and 4:15 p.m. on October 12, investigators said Monday. The third final derailment occurred just around 5 p.m. at the Arlington Cemetery station. A total of 187 people aboard the train had to walk through a dark tunnel about the length of six football fields to get to safety, NBC Washington reported.

Investigators said that the third rail, which is electrified and brings power to the trains, was damaged during the derailment and could've led to a fire.

No one was seriously injured in the derailment, although one person went to the hospital, according to NBC Washington.

The Washington Metrorail Safety Commission late Sunday announced it directed WMATA, the agency that runs Metro, to pull all of its 7000-series rail cars, which are manufactured by Kawasaki Rail Car, Inc and are the newest in Metro's fleet. They first began operating on the system in 2015, replacing aging trains on the city's decades-old subway system.

The move has temporarily eliminated 60% of Metro's fleet, leading to delays on the system Monday with trains scheduled to run on all lines just every 30 minutes. Some Metro customers took to social media during their commute Monday morning to complain of jam-packed stations trains and their delayed arrival. According to DCist, some trains took as long as an hour to arrive Monday.

"We want the public to know we are committed to their safety and will continue to release updates as we receive them," WMATA said in a statement on Twitter.