SAN FRANCISCO -- A preliminary investigation into a crash between two San Francisco Municipal Railway trains over the weekend that sent a dozen people to area hospitals indicates one of the trains was speeding, according to Muni officials.

The crash occurred at about 2 p.m. Saturday at Fourth and King streets, one block south of AT&T Park.

According to Muni officials, a one-car, T-Third train going west on King Street between Third and Fourth streets rear-ended a two-car N-Judah train that was stopped at the Fourth Street traffic signal. The back of the N-Judah train was heavily damaged in the crash.

"Based on the investigation so far, it appears as though the T-Third train was traveling at 17 mph," Muni spokesman Judson True said. He said that section of roadway is a 3-mph zone for Muni trains.

Muni was also investigating whether the T-Third operator may have been on a cell phone at the time of the crash.

Video footage taken just after the crash shows the operator with a cell phone in his hand when he went to check on passengers, but is inconclusive as to whether he was on the phone before the crash, according to Muni officials.

Investigators were seeking to review the operator's cell phone records, True said.

According to Muni and the San Francisco Fire Department, 16 people were injured in the mid-afternoon crash, and 12, including the two Muni drivers, were hospitalized.

According to San Francisco Fire Department, the various injuries ranged from minor to potentially life-threatening.

Four of the injured were reportedly released from San Francisco General Hospital the same day, Muni reported.

Both train operators have been placed on standard administrative leave and investigators are also awaiting the results of drug and alcohol testing.

The T-Third train operator has been a light-rail operator since 2004; the N-Judah operator since 2007, Muni reported.

Any possible disciplinary measures would be taken after the investigation is complete, according to True, who said more information may become available later this week.