One day before he was scheduled to receive a safety award, a Green Line operator at the controls of an outbound trolley slammed into a waiting trolley at Boylston Street Station Thursday. The crash sent 37 people to area hospitals with minor injuries and shut down service on the Green Line’s busiest section for about three hours, officials said.

MBTA inspectors ruled out track and signal problems and were continuing to investigate whether the crash — which they likened to a rear-end fender bender at a stoplight — was caused by equipment failure on the 25-year-old trolley or by the driver, said T spokesman Joe ­Pesaturo.