A Massachusetts Bay Transportation Authority bus hangs over the Massachusetts Turnpike after crashing on Centre Street in Newton, Mass., Sunday, May 18, 2014. Seven passengers and the bus driver were transported to a hospital with non-life-threatening injuries, MBTA spokeswoman Kelly Smith. Three other passengers declined medical treatment. (AP Photo/Boston Herald, Matt Stone)
A Massachusetts Bay Transportation Authority bus hangs over the Massachusetts Turnpike after crashing on Centre Street in Newton, Mass., Sunday, May 18, 2014. Seven passengers and the bus driver were transported to a hospital with non-life-threatening injuries, MBTA spokeswoman Kelly Smith. Three other passengers declined medical treatment. (AP Photo/Boston Herald, Matt Stone)
A Massachusetts Bay Transportation Authority bus hangs over the Massachusetts Turnpike after crashing on Centre Street in Newton, Mass., Sunday, May 18, 2014. Seven passengers and the bus driver were transported to a hospital with non-life-threatening injuries, MBTA spokeswoman Kelly Smith. Three other passengers declined medical treatment. (AP Photo/Boston Herald, Matt Stone)
Richard Donohue, the Massachusetts Bay Transportation Authority officer wounded during the shootout with the Boston Marathon bombing suspects, waves a "Boston Strong" banner as his wife, Kimberly, raises her arms during ceremonies prior to Game 3 of the Eastern Conference finals in the NHL hockey Stanley Cup playoffs between the Boston Bruins and the Pittsburgh Penguins, in Boston on Wednesday, June 5, 2013. (AP Photo/Elise Amendola)
In this 2010 photo provided by the Massachusetts Bay Transportation Authority, Richard Donohue Jr., left, and Sean Collier pose together for a photo at their graduation from the Municipal Police Officers' Academy. On Thursday, April 18, 2013, Massachusetts Institute of Technology Police Officer Collier was fatally shot on the MIT campus, and transit police officer Donohue was shot and critically wounded. Authorities allege that Boston Marathon bombing suspects Tamerlan and Dzhokhar Tsarnaev were responsible. (AP Photo/Massachusetts Bay Transportation Authority)