Transit officials in Boston say an underground crash of commuter trolleys was caused by one driver text messaging.

Police said one trolley slammed into the back of another that was stopped at a red signal, waiting to enter Park Station on Friday evening.

Forty-nine people were hurt but none of the injuries is considered life-threatening.

A senior transit official is quoted as saying the driver of the trolley that hit the stationary one admitted to police he was text messaging at the time of the crash.

The 24-year-old driver was texting his girlfriend, according to the Boston Globe newspaper.

Daniel Grabauskas, general manager of the Metropolitan Boston Transit Authority, said the operator told detectives that, when he looked up from text messaging, "it was too late as he applied the brake and the train struck the other trolley."

"It's difficult for me to contain my outrage," Grabauskas told the Globe, adding that the driver will probably be fired.

The driver has worked for the transit authority for two years.

Grabauskas said damage was limited to one end of the moving trolley and one end of the other one. Each trolley had two cars.

With files from The Associated Press