On Muni's older Breda trams the interlock had a little toggle switch on the circuit breaker panel (conveniently located in the cab) you could use to override it

On Muni's older Breda trams the interlock had a little toggle switch on the circuit breaker panel (conveniently located in the cab) you could use to override it. On the newer ones, it looks like the doors didn't detect a "pinch", the interlock decided the doors were closed enough, and the driver couldn't be bothered to check the video cameras.