State House News Service Photo

Shuttle buses will replace a stretch of Orange Line train service for the next three weeks while MBTA crews replace a track switch damaged during a Tuesday derailment, and all new trains on the Orange and Red Lines will be taken out of service for an investigation, the T announced.

Buses will continue to run between Oak Grove and Sullivan Square stations for three more weeks while workers replace the decades-old switch. The T described the switch as “significantly damaged” due to the slow-speed derailment at Wellington Station.

Ridership is way down during the pandemic, hovering around 25 percent of the roughly 208,000 average weekday trips on the Orange Line taken in February 2020, but tens of thousands of travelers will likely be affected by the disruption in service.

In addition to fixing the switch, the T plans to make “additional infrastructure upgrades and improvements” at other Orange Line stations during the shutdown, the agency said.

Investigators have not determined the cause of the derailment, which occurred while one of the four new Orange Line trains was crossing from the northbound track to the southbound track to accommodate a work zone. None of the roughly 100 passengers on board nor any workers were injured.

The MBTA will pull the remainder of the new Orange Line and Red Line cars manufactured by CRRC MA from service for an unspecified amount of time to examine whether anything related to the vehicles contributed to the derailment.

Officials removed new Orange Line trains from service on at least three prior occasions: in September 2019 after a door leaf opened mid-trip, in November 2019 due to a faulty pad interface creating noise, and in March 2020 because of a problem with faulty bolsters.

A high-profile Red Line derailment in June 2019, which prompted the appointment of an outside panel to review the MBTA’s safety, created months of delays because the careening train destroyed a signal bungalow and damaged two others.