MBTA officials said Monday that they have suspended the driver of a Green Line trolley after a preliminary investigation found he was to blame for a derailment on Saturday that injured 11 people.
Deputy General Manager Jeffrey D. Gonneville said the accident happened as the outbound D Line train had just left Kenmore Station with 150 passengers at about 11 a.m. The driver was approaching a signal that marks where the C and D lines split, near Beacon Street and Commonwealth Avenue.
The train derailed when it continued rolling through that section of track and drove over a switch that was in the process of moving from the C Line to the D Line, Gonneville said.
Gonneville would not say how fast the train was going or what may have led the driver to lose control of the train. Investigators have ruled out mechanical problems with the track, the switch, and the train itself and have concluded the accident “does appear to be operator-related,” Gonneville said.
A passenger, Bryan Marden, told the Globe over the weekend that the train struck the side of the subway tunnel, throwing passengers to the floor, and then came to a sudden stop amid a cloud of dust and debris.
The 62-year-old driver, who suffered a leg injury and bruises, was among the 11 people injured. He remained hospitalized on Monday, Gonneville said. The driver, who was hired three years ago, was on his regular route and familiar with that section of track, Gonneville said.
The Boston Carmen’s Union, Local 589, which represents MBTA employees, declined to comment, saying it had not seen any information related to the investigation.
Boston EMS transported 10 people to hospitals, some with serious injuries. The agency said Monday that it had no further information about their conditions.
The derailment forced the MBTA to run buses along parts of the C and D lines on a particularly busy day, as it was transporting thousands to a Red Sox double-header and the Boston Pride Parade.
General Manager Steve Poftak, speaking at an MBTA board meeting Monday, offered his thanks to the workers who moved quickly to set up bus service after the derailment.
“Obviously, the incident on Saturday is regrettable,” Poftak said. “Obviously, we regret the impact on our riders and the disruption of service on what was a busy day here in the city. Safety remains our first priority here at the MBTA.”
The Green Line derails more frequently than the Red, Orange, and Blue lines, according to MBTA data. Over the past 20 years, the number of derailments on the line has fluctuated from a high of 12 in 1999 and 2000 to a low of two in 2012.
Saturday’s derailment was the third this year. The first occurred Feb. 5, the day of the Patriots Parade, near the Beaconsfield stop in Brookline. Fifty passengers were evacuated; none were injured. An initial investigation identified a “track defect” as the probable cause.
The second happened March 30, when a Green Line train that was not in service was crossing over a switch.
On Monday, Gonneville sought to reassure the public that derailments are rare.
“Our message to commuters is our system is safe,” Gonneville said. “This is a very serious matter that we are taking seriously, and we are going to take any necessary corrective actions that come from this investigation.”