MBTA investigators are focusing on the driver in Thursday’s Green Line crash that sent 37 people to hospitals with minor injuries and shut down the heart of that subway line for three hours, finding no fault with the equipment, officials said Friday.

“We have ruled out both any mechanical issues for either of the trains or infrastructure -- meaning track, signals, etc. — and so at this point we’re now focused on the operator,” Secretary of Transportation Richard A. Davey told reporters. “We will continue to interview the operator over the next couple of days to see exactly what happened.”