BOSTON (AP) — A charter bus carrying high school students from Pennsylvania crashed when it attempted to pass under a low bridge in Boston on Saturday night, injuring more than 30 people, four seriously, and leaving some trapped for more than an hour, authorities said.

The students had been in the area to visit Harvard University. The bus, which was carrying 42 students and adult chaperones, was heading back to the Philadelphia area when it struck an overpass on Soldier's Field Road, a major crosstown road, at around 7:30 p.m., Massachusetts State Police said.

Authorities said the Calvary Coach bus did not belong on the road, where a 10-foot height limit is in place and over-sized vehicles are not authorized. State Police said the driver, whose name was not released, "failed to heed signs" warning of the height limit and will likely be cited for an overheight violation. The investigation will determine if he faces more serious charges, state police said. The driver was not injured.

Ray Talmedge, owner of the Philadelphia-based Calvary Coach Bus company, said Saturday night that his driver was being interviewed by police. Talmedge, who said he didn't know anything about the road restrictions, said the driver also drives a school bus.

The students were part of a Destined for a Dream Foundation group, Talmedge said. Officials with the Bristol, Pa.-based group, a nonprofit that helps underprivileged youth, refused to comment on the crash when reached by phone.

The group's Facebook page said the trip to Harvard was to "visit the campus, sit with the office of cultural advancement, followed by a tour of the campus ... followed by Harvard Square (shopping, eating, site seeing...etc...) This should be a fun time for all!"

The bus suffered significant damage in the crash. The front part of the roof was pushed in while the center section bowed downward. Photos posted on the Fire Department's website showed firefighters standing on the top of the bus using boards to extract people. The last victim was freed from the bus around 9 p.m., according to the department.

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The Boston Emergency Medical Services said 34 people were injured, including one who was hospitalized with life-threatening injuries and three with serious injuries. None of those injured were identified, and state police said they did not know how many of the injured were adults and how many were juveniles.

The Massachusetts Bay Transportation Authority sent buses to pick up other passengers and get them out of the frigid temperatures.

Soldiers Field Road curves along the Charles River and passes by Harvard and Boston University. It is a major roadway to the Massachusetts Turnpike. Soldiers Field remained closed while tow trucks tried to hoist the bus over guardrails onto an adjacent road.