I believe the solid Realtrax is out of production now and it is all hollow. But you can find a lot of it on thebay and of course other places. I personally dislike the hollow track and I made sure when I bought mine it was all solid. I DID find many problems with the tabs welds where they did not make good electrical contactto the rails and I had to test each track piece for good connections. This problem was found on many many NIB Solid Realrax. Once fixed, I had no signal or operational issues.