MEDFORD, MASS. (WHDH) - Crews responded to a trolley fire on Interstate 93 in Medford Saturday.

The trolley was fully engulfed according to police who had trouble getting to the scene due to heavy traffic.

Officials are unsure how the fire started, but the driver said he heard a loud bang.

“The driver mentioned that there was a loud bang,” Deputy Fire Chief Brian Cronin said. “He looked down and there was fire coming up through the floor and he was able to get the vehicle off to the side of the road.”

All passengers were able to exit the trolley safely.

An investigation is underway to determine the cause of the fire.

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