A passenger filmed an apparently sleeping driver on the Croydon tram network.
Drivers say a “dead man’s handle” safety device often does not stop trams when drivers fall asleep.
Police want to speak to three people in connection with the assault on the Kurdish-Iranian victim.
Those involved in the south London attack on a Kurdish Iranian are labelled “scum” by the local MP.
The 17-year-old is in a “serious but stable condition” after the assault at a bus stop.