@sidereal Wouldn't "safe halt" be very much dependent on the speed of the trolley? I'm thinking of the cause of the train crash in Germany in the 90s in Eschede where a bullet train accident caused some of the carriages to be switched over at speed onto another track before carnage ensued. If this trolley went at high enough speed the conundrum still prevails but it has one more possible solution, which *may* kill no one but that's hard to tell. (I'm saying add a speed indicator to the meme😉)