I've been thinking about the 'trolley problem'. The trolley in San Francisco has a top speed of 9.5 mph (15.3 km/h).
It should be possible to throw the leaver between the times that the front and back wheels pass the switch. With the front wheels going one direction and the back wheels going the other, the trolley should stop.
Worst case: the trolley derails, falls over sideways and kills everyone inside the trolley and everyone tied to the track.