CAMBRIDGE, MASS. (WHDH) – As federal investigators began work Wednesday, outside experts and elected state officials shared their response to the Green Line train derailment that sent seven people to the hospital Tuesday afternoon.

No one was seriously injured in the incident near Lechmere train station. However, speaking to 7NEWS, transportation safety expert Keith Millhouse said it could have been worse.

“You will notice that the lead car has been pushed onto an adjacent track. “So if that track was an active track and a train was coming in one direction or the other at that time, there could have been a collision between two trains, which would have had a more devastating impact,” Millhouse said.

The derailment is the latest problem on the Green Line Extension, the newest part of the MBTA system. It extends the northern end of the Green Line from Lechmere to Union Square in Somerville and College Avenue in Medford.

The expansion was already facing a two-week shutdown last year when it became apparent that the new tracks were too narrow.

State Rep. Mike Connolly’s district includes the Green Line extension and portions of the Red Line.

“We have made great progress in reducing these slow zones,” he said, referring to sections of the route where trains must operate at reduced speeds. “So the fact that something new like this happened yesterday is really disappointing.”

Derailments across the MBTA system have dropped from more than 20 per year five years ago to just two to three per year. But the fact that they keep happening could be why National Transportation Safety Board investigators are taking a closer look, Millhouse said.

“The quality control that needs to be put in place for inspection to ensure we don’t have a pervasive problem on this line could unfortunately take some time,” he said.

Although MBTA investigators were quick to point out that human error could be behind the recent problem, experts say that doesn’t rule out underlying problems that may need to be addressed.

“The question arises as to why human error continues to occur in the T-System. They shouldn’t happen. These operators need to be monitored. They need to be properly trained and control systems should be in place to prevent such human errors from occurring,” Millhouse said.

NTSB officials said it could take a month for the preliminary investigation to uncover the cause of the derailment and a few years for them to reach a final answer.

As of Wednesday evening, it was unclear how far the investigators’ investigation had progressed.

With the derailed train still parked on the tracks near Lechmere, the incident has resulted in an indefinite suspension of service along the Green Line Extension. T officials said it is unclear how long shuttle buses will replace train service on the extension.

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