Train Script Problem

[Gunderak]

Basically im making a train that moves on tracks by its self, but iv ran into a problem.
the tracks are npcs that set images to whatever track piece it is.
is there any way to check if a npc is touching a certain npc and set its this.mode = whatever depending on whats in the npc its touching?
thanks in advanced.
im sure theres a way to do it