The MBTA is looking into the issue of “cascading failures” and the systemwide impact of breakdowns as a rocky two weeks of service continued this weekend with a pair of derailed Green Line cars.

“The secretary has instructed the MBTA, as part of its review of the incidents in the last week, to evaluate whether there were steps that could have been taken to avoid ‘cascading failures’ impacting customers of the trains not disabled,” T spokesman Joe Pesaturo said, referring to Transportation Secretary Stephanie Pollack. “Per her direction, Keolis and MBTA staff will perform such evaluations.”

Two weeks ago, a wheel broke off of a crowded Commuter Rail train car on the Fitchburg Line, causing it to derail. Just two days later, a supercharger failure started a small fire in a Commuter Rail locomotive heading to Boston from Kingston. No one was hurt in either case, but hundreds of people’s commutes were put on hold as delays rippled out from the incidents.

This Saturday, two out-of-service Green Line cars hopped off the tracks on the Green Line’s B branch. Again, no one was hurt, but T data shows reliability suffered greatly along much of the Green Line. On the B branch, only 57 percent of trains arrived on time, down from the 30-day average of 75 percent and the goal of 90 percent.

The T is still investigating the cause of the Green Line derailment.

Paul Regan, executive director of the MBTA advisory board, said the fact that much of the system has a single track makes for few options when a train breaks down.

“Any significant delay for a train and you’re really out of luck,” Regan said.

Pesaturo said, referring to Keolis Commuter Services, which operates the Purple Line, “Keolis and the MBTA work hard to train personnel to swiftly identify the cause of a mechanical problem and quickly address it in an effort to move a disabled train as soon as possible … If a train can’t be moved on its own, a second train will be attached to the disabled train in order to push or pull it out of the way.”

Pesaturo said the $8 billion the T is investing in its aging infrastructure will help with this and other issues. The T is adding a second set of tracks to some of the more popular Commuter Rail lines, which would allow workers to get a busted train out of the way.

“The T is also aiming to sharpen its personnel’s troubleshooting skills in order to shorten the time necessary to get a disabled train off the main line,” Pesaturo said.