In this photo released by the Boston Fire Department via Twitter, firemen work to remove injured passengers from a bus that hit an bridge as it traveled along Soldiers Field Road in the Allston neighborhood of Boston Saturday night, Feb. 2, 2013. Officials said the bus carryinyg 42 people was traveling from Harvard University home to Pennsylvania when it struck the overpass. (AP Photo/Boston Fire Department)

In this photo released by the Boston Fire Department via Twitter, firemen work to remove injured passengers from a bus that hit an bridge as it traveled along Soldiers Field Road in the Allston neighborhood of Boston Saturday night, Feb. 2, 2013. Officials said the bus carryinyg 42 people was traveling from Harvard University home to Pennsylvania when it struck the overpass. (AP Photo/Boston Fire Department)

In this photo released by the Boston Fire Department via Twitter, firemen work to remove injured passengers from a bus that hit an bridge as it traveled along Soldiers Field Road in the Allston neighborhood of Boston Saturday night, Feb. 2, 2013. Officials said the bus carryinyg 42 people was traveling from Harvard University home to Pennsylvania when it struck the overpass. (AP Photo/Boston Fire Department)

In this photo released by the Boston Fire Department via Twitter, firemen work to remove injured passengers from a bus that hit an bridge as it traveled along Soldiers Field Road in the Allston neighborhood of Boston Saturday night, Feb. 2, 2013. Officials said the bus carryinyg 42 people was traveling from Harvard University home to Pennsylvania when it struck the overpass. (AP Photo/Boston Fire Department)

Emergency personnel remove passengers at the scene of a bus crash, Saturday, Feb. 2, 2013 in Boston. Authorities say a charter bus heading from Harvard University to Pennsylvania has struck a bridge in Boston, injuring 33 people. (AP Photo/The Boston Herald, Stuart Cahill) BOSTON GLOBE OUT; METRO BOSTON OUT; MAGS OUT; ONLINE OUT