As an Engineer with a Physics background I say the most ethical choice is the real numbers side as the tram, having no room to accelerate between victims, will quickly stop, whilst it’s more likely it can keep going for ever on the integer branch of the line.

A more effective vehicle for this would be a tank or maybe a steamroller.

(Note to self: keep this in mind if I ever become an Evil Overlord and need to execute large numbers of people in a gruesome manner)