Okay, I've been looking at the NMRA site and here and I can't find the rail center for a prototypical ladder yard. I'm using Atlas#7 turnouts. I'd like the yard track a little narrower than the main line.
One thing to remember...you need room between tracks to get in there and get cars that may have derailed. I am using Unitrack #6 turnouts and it leaves just enough room to get my thumb and index finger in between tracks and cars. I have lots of photos of real yards and those tracks are close together. But I dont believe they have the derailment problems we encounter with our models. JMO
My yard track centers are 1 1/4". I used Atlas #7 switches, separated on the ladder by a single 2" piece of Code 55 straight track. A 1" center spacing would more closely match prototype (about 13 feet), but as George pointed out, you need room to stick a few prototype-sized fingers in-between tracks to re-rail cars, etc. Here is a photo of the east end of my yard under construction, and then another photo of the yard after completion. I think the 1.25" spacing looks fine after ballasting/scenery work. If you wanted the spacing closer, however, then you could omit or shorten the 2" "spacer" track between turnouts, and it would close up the center-to-center spacing. John C.