Photo courtesy of State House News Service.

It’s been a bad week for the MBTA; first investigators discovered the agency spent $100,000 on a private bathroom, and then a train derailed.

Calling Wednesday’s Red Line derailment “not acceptable,” Gov. Charlie Baker said yesterday a next step for MBTA officials will be to determine exactly what occurred and make sure similar issues aren’t present elsewhere in the subway system.

“I think the most important thing from our point of view is that nobody got hurt, and credit to the T folks, they had the system back up and operating again by six o’clock last night, and this morning went relatively uneventfully,” Baker told reporters after speaking at a Washington Post Live event on opioid addiction. “But they need to do some homework on why this happened and figure out if there is some issue that needs to be considered along the rest of the lines and the rest of the tracks to make sure that we don’t have some terrible situation like this lurking somewhere else on the tracks.”

A portion of the Red Line was shut down Wednesday after a train derailed as it approached Andrew Station, resulting in damage to about 300 feet of the third rail. The T said the train operator reported an indication of motor failure in the train’s last car as it arrived at the station. Passengers fled the smoke-filled station, and were diverted throughout the day to shuttle buses and in some cases encouraged to make their trips via commuter rail.

Baker said 40 buses were used to shuttle Red Line riders, and that Boston police were “terrific” in opening up traffic lanes for those buses to use.

“As I’ve said many times, most of the stuff on the tracks and the systems and the trains and the cars and all the rest on the T are 50 years old or more,” Baker said. “For decades people neglected making the investments they should have been making in the core system. We’re investing hundreds of millions of dollars in those core system upgrades, and a couple years from now, you’re going to have basically new cars on the Red Line, new cars on the Orange Line, new signals and switches on both systems, new cars and a very different system than the one we have now, but in the meantime, I get the fact that what riders had to put up with yesterday was unacceptable.”

Newton Democrat Setti Warren, a candidate for governor, on Wednesday called the derailment “further evidence that [Baker] is failing and his strategy of no new revenue and privatization is wrong.”

Baker’s “failure is causing declining ridership, forcing people into cars and compounding the traffic gridlock spreading in all directions,” Warren said in a statement. “The Baker administration claims they are making improvements that riders can’t see (WHAT does that even mean?) and that we should be patient because it will take 20 years to fix the T. That seems right – it will take 20 years, if we leave him in charge.”

Boston Mayor Martin Walsh, who also spoke at the opioid event, said service has improved on the MBTA and “major investments” have been made in the Red Line, which he said has “probably been one of the highest performing lines of the system consistently over the past year.”

A former state representative, Walsh said the state still needs to invest more in its transportation infrastructure.

“They need a dedicated revenue source, and they’ve got to figure out a way of doing it, and it’s not going to be done by fares, it’s not going to be done by advertising,” Walsh said. “I think the governor has done an awful lot of work on the T. This situation that happened yesterday, we really haven’t heard something like this in quite a while, that we’ve had a big breakdown like this.”

Walsh planned to meet Thursday with MBTA general manager Luis Ramirez.

Wednesday’s incident comes a few months after a commuter rail car broke free from a moving train.