My accident was at an intersection where there is a street camera (not red light camera) right above. The video is the only thing can show that I was not at fault.
The California Department of Transportation website states " . . . that Caltrans does not save traffic video and is unable to provide archived footage." Notwithstanding the same, a subpoena could potentially be issued in a case requesting the production of the video footage. If the video footage does not exist, the custodian of record should respond that they are unable to provide the footage.
The video can be obtained either through request or subpoena, depending on their policy. In any event, send out a notice to preserve evidence via certified mail, return receipt requested, giving the specific location of the camera and date and time of the accident. These cameras often overwrite themselves after a short period of time so you need to act quickly to preserve that footage. Follow up with them a week or so after you send the letter to make sure they are preserving the evidence. Then you can worry about how to get a copy of the tape.
An attorney would have to subpoena the film. But the case would have to be in litigation to do this. Also it is very important to write a letter to DOT asap asking them to save this tape, they are only kept for a certain time. Also you need to find out who has the film. It could be the city, county or state.
You didn't mention if you are injured. If your not and you are just trying defend yourself you need to talk to you insurance company. I personally doubt they will even bother unless there are major injuries.