My elevated section also has a large plywood top that uses in part dowel supports similar to valllieone above to support the weight of a D56 city. My plywood just sits on the dowel tops. My plywood is not going anywhere due to the city weight and the fact that it is trapped by elevated track. The dowel bottoms are glued and screwed to level one of my layout. Under Grand Central Terminal in my city are representative tracks complete with platforms, people, etc. There is also track 61 complete with FDR in his wheelchair and limo. I use PVC pipe with flange bases painted black as supports on the GCT track platforms. The flange bases are hidden under the track platforms. The PVC pipe is the conduit for the substantial wiring required to implement my city scene. My D56 city is power by 12 VDC using LED lighting.