Spacing: 2" minimum on straight track in yards, significantly wider on curves depending on radii. Why: cause John Armstong told me to in his book Track Planning for Realistic Operation. Just starting a new layout - no track laid yet - but here from previous layout ( think I went 2 1/16" centers here: I used more generous spacing on the curves in staging to make sure no risk of side swiping longer cars - it's variable but at minimum 2 1/4 and larger.
I use the same separation as is required by the W/S #6 double-crossover; 2.0". I do the same in yards.
Buy the Armstrong book, it's worth the money and the read. We use 2-1/8 on straight, 2-1/4 on curved.
you don't need much more than two inch, unless you have fat fingers that you want to get in ... i use 2 1/4 on straights, and 2 1/2 on 20 inch curves
The NMRA 2x4 Module standard uses 2 inch track spacing, which seems to be pretty widely accepted. If you want to get extremely accurate, this BNSF PDF shows a table on page 70 with track spacing data. Most states require at least 14’ between track centers. The last line of the table shows ‘BNSF standard’ and they specify 25’ spacing. That wide spacing is probably more common in rural areas; I know the triple track main near me is not that spread out. Keep in mind, this is for new construction only; older existing track can keep whatever it already has. https://www.bnsf.com/ship-with-bnsf/ways-of-shipping/pdf/indytrkstds.pdf
So if you do the math, 14 foot centers translated to HO is 1.931 inches or a hair less than 1 15/16 inches. So 2-inch centers in a yard is comes out to 14.5 scale feet. Now on curves, the sharper the curve, the more you will need to increase the track center separation to prevent long rolling stock from interfering with each other. From memory, if you are using fairly broad curves, such as 30 inches and above, you may be ok with 2 1/4 inch centers, but test to be sure your longest rolling stock clears each other.
another 2" on straights here that BNSF document looks like an interesting read and good info. As ever standards change and in older times I think the norm was less than 14'. again things vary based on location, age and RR. From a modelling point of view 2" just works, and wider on curves to suit your space and stock.
About 2 1/8" on straight, narrowing to 2" at bridges. 2 1/4 to 2 3/8" on curves. Staging yard is just that staging which means "manual" switchers. I use 2 1/2"+ in the staging yard to get fingers in between the cars when necessary. %5BURL=https://www.trainboard.com/highball...4babc7b02d51bd46372c574f0817d.jpg[/IMG][/URL]
