The MTH signal bridge is a copy of a PRR Lines West bridge and used about Pittsburgh and all tracks going west. The Plasticville bridge is a good scale model of the PRR Lines East bridge (if one removes the vertical members in the bridge truss). You can get working signal heads from Custom Signals or MTH. The Custom Signals line has been sold to Atlas and the excess inventory is for sale on ebay. People of spliced the Plasticville bridge to span as many as 4 tracks.