so the 3-railers cannot be dubbed as being non-prototypic after I came across that T. O'Sullivan photo. All wood with what seems to be angle iron lining. Wonder how they picked up the current from the center rail...
Looking closely at the photo, you can make out the cable for the lower tram car next to the center rail. at the top of the photo is the upper tram car approaching the loading bin. A passing track behind the photographer would allow the
two cars to pass. The center track would be split into two and the outer rails moved out for the cars to pass.