A post crash video from inside the train shows the severity of that crash, as well as the operator of the train that caused the accident using a cell phone.
It is unclear whether he was on the phone during the crash or pulled it out afterwards to call for help. Two sources with knowledge of the investigation told us that preliminary findings lead to the likelihood of human error.
Police said Saturday the train operator blamed the accident on a sudden power surge.
"We've been told the operator prepared to stop however the train surged forward and that train rear ended the train that was stopped for the red light," says Captain David Lazar of the SFPD.
However, Muni inspected the wreckage and found there was nothing wrong with the brakes.
The preliminary findings also show the operator was speeding, going more than five times the speed limit, traveling 17 mph in a 3 mph zone.
16 were injured when a T-Third street light rail vehicle slammed into the back of a two car N-Judah train on King Street, between 3rd and 4th. The N-Judah was stopped at a red light.
Dr. Andy Frank is a renowned expert in mechanical engineering and ground transportation. He says he's never heard of a power surge causing brakes to fail.
"The reason why it's unlikely is that most control system are designed so that power surges cannot come in and cause that kind of problem," says Frank.
Muni's light rail vehicles also have two emergency braking systems. One is on what's called a T- handle which controls the acceleration. On that handle is what Muni operators refer to as a "dead man", a feature which immediately stops the train. Operators can also punch an emergency stop button on the console.
Investigators have concluded that the operator did not press the emergency button on the console. No word yet if he used the dead man lever.
Both operators were tested for drugs and alcohol but the Muni says those results are not in yet. Investigators are also trying to get the operators cell phone records to see if he was on the phone at the time of the crash.