The only thing i have ever made out of the sign in the tunnel was... that the only place zombies CROSS over to you would be where? think about it.... THE POWER ROOM NEXT TO THE LAVA PIT.. & what spawn underneath of the broken catwalk that zombies jump across to get to you.. ELECTRICAL WIRES!! So just another bold theory. Can those power wires be used elsewhere? Like possibly underneath the tower? or hell maybe even in the bus?