BOSTON (WHDH) - As the investigation into the Green Line crash gets underway, a transportation expert sat down with 7NEWS to break down what officials will be looking for.

Dr. Carl Berkowitz said the type of crash that occurred on the B branch of the Green Line train Friday evening is a rare event that should never happen.

RELATED: ‘This shouldn’t happen’: Officials investigating Green Line trolley collision in Brighton that left 23 hospitalized

“Well, the first thing you do is you empty the train get rid of the passengers and you take the train driver for an alcohol and drug test. That’s the first thing they do,” Berkowitz said. “Then we want to see if the vehicle goes into the shop and the vehicle is checked to see if the brakes are working properly. From what I know about the MBTA, they have one of the best inspection systems in the country. So, I doubt that it was the brakes or something of that nature.”

Emergency crews were called to the scene of the crash which occurred along Commonwealth Avenue near the Agganis Area around 6 p.m. and transported the victims to area hospitals. Firefighters confirmed that all 25 suffered non-life-threatening injuries.

The driver of the trolley was among those transported.

MBTA General Manager Steve Poftak said that for reasons still unknown, one trolley rear-ended another and the force of the collision derailed the train cars causing significant damage to the infrastructure.

“We will obviously get to the bottom of this. This shouldn’t happen and we will find out why it happened and we will ensure that it won’t happen again,” Poftak said. “As a tertiary matter, once we are satisfied that we have all the information we need from the scene behind us, we will begin the process of rerailing the vehicles and also making any repairs to the infrastructure that needs to be made.”

RELATED:‘Boom!’: Green Line passenger recalls startling trolley collision

This is not the first time a serious crash has been reported on the Green Line.

In May of 2008, an MBTA operator was killed when the trolley she was driving slammed into the back of another in Newton. In that instance, both trains also derailed and several people were hurt.

Investigators said the operator ran through a red light at high speed hitting that other train.

Just one year later, another collision occurred between the Park Street and Government Center stations. Nearly 50 people were injured and investigators determined one of the operators was texting at the time of the crash.

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