code/modules/transport/tram/tram_structures.dm

/obj/structure/tram	the tram has a few objects mapped onto it at roundstart, by default many of those objects have unwanted properties for example grilles and windows have the atmos_sensitive element applied to them, which makes them register to themselves moving to re register signals onto the turf via connect_loc. this is bad and dumb since it makes the tram more expensive to move.