Well, you have not stated what gauge the track is, or what scale your locos are .... The only advice I can give you is the BR standard 6 feet between two sets of rails. I use 150mm between centres -but I am a 16mm scale modeller.
Assuming Gauge 1, that almost all of us run, the typical LGB spacing for back-to-back, 8-foot diameter (1600-series) turnouts is ~7-3/4 inches center-to-center. This is adequate for most anything on the straights.
Posted By Jerry Barnes on 02/15/2008 3:32 PM
If you are doing 1/20th narrow gauge, you would probably have to go to 10" at least, if planning a K-27, perhaps a bit more? Jerry
One of our club members triple heads Accucraft K-27s and they fit through his LGB truss bridge that is 6-1/2" wide. He says that the doesn't buy the K-38 because it won't quite fit through, so I would think that it is less than 7-1/2" wide. Of course that is on the straights, and curves need more space for the overhang.
On our new club track, the plans call for 9" o.c. spacing with 20'dia. track. That should be enough for three K-36's passing on the curves. Now, 7/8's would be another story. /DesktopModules/NTForums/themes/mls/emoticons/tongue.gif
I am planning my layout which is gauge 1 track running 1:20.3 scale equipment at 8" center line to centerline on the straight away and 10" center line to center line on the curves. Most of my curves are 8' radius but a few are 6' radius.
I am using 8' diameter track. Switches are Aristo 10'. I purchased 2 parrell adadpers and created a siding with the 8' curves. I am 8 inches on center. Works great with 1/29 stock. I will occasionally use my Bachmann Annie and still have no trouble passing parked stock.
I am using 1:20.3 and use 6.5" Center to Center on Straights, though I am only running 2 short ovals at this time, but running 2 trains at the same time hase not yet caused a problem, I will start the larger setup outside this year and will have to gauge my Center to Center on the curves I use then.