BOSTON (CBS) – Three people were injured when two Green Line trolleys collided on Huntington Ave Monday afternoon.

MBTA spokesman Joe Pesaturo says the accident involved human error. “We know that the switch was in the wrong position,”  says Pesaturo. “That’s the cause of this accident, it had nothing to do with infrastructure or the vehicles.”

WBZ NewsRadio 1030′s Lana Jones reports

The man responsible for putting that switch in the wrong position has been with the MBTA for almost 20 years. He has been interviewed by investigators and will undergo mandatory drug and alcohol testing.

Two passengers and a trolley operator reported having back and neck pain after the crash.

There were 24 passengers on the trolley going outbound, and no passengers on the trolley headed inbound.

One of the two passengers who went to the hospital after being injured on the train was Wessam Paki. He had just fallen asleep, when he woke up to find other passengers falling on him. He tells WBZ that the passengers accidentally forced his head into the wall; his arm and leg were also injured.

Paki was so shaken by the experience, he says his head was swimming, “You know what I mean, for the first couple hours I [couldn't] talk,” he explains.

Due to the accident, bus service is being provided between Northeastern and Heath Street on the E Line. Service is not expected to be restored until Tuesday.

WBZ-TV’s Jim Armstrong contributed to this report.