Quote from SDL39FAN on June 5, 2017,
One, the original article is from 1975 so are the parameters used by the author still valid today or have there been changes that would look at this in a different way?
<snip>Would it be possible to put four tracks side by side in a 24-30 inch wide shelf with room for a siding on each side?
NMRA standards have been updated and they are available online for downloading - especially the ones on track clearances (S7 and S8 IIRC). I model P:48 and the straight yard tracks are centered at 3.75" and there is plenty of room to uncouple cars with a magnetic wand from the top. If I were using Protocraft couplers with cut levers, it might be a different story. I would suggest a mock up, with the tracks at the layout's planned height, lay out 6 pieces of flex track at various distances apart and try coupling and uncoupling with whatever couplers and tools you plan to use. Can also move the tracks back various distances from the edge to judge how easy it is to reach across - especially when the closer tracks are loaded with cars (article mentioned they stored cars on nearly every available siding).
Consider the era too - 40 footers and first generation diesels can handle curve radii of 40". But....can you couple and uncouple on those curves?
LD Sig published some suggestions that Joe Fugate mentioned in one of the TrainMasters TV videos recently:
Operational length of car (middle of coupler to coupler distance)
Radius = 2.5 x Op Length can track, but pushing it
Radius = 3 x Op Length Run freely, but toy looking as radius appear too tight
Radius = 4 x Op Length Looks good
If curve viewed from inside, this can decrease to 3.5x
Radius = 5 x Op Length Ease of coupling and switching
They found that a radius of 5 times the operating car length allowed you to couple and uncouple - anything less than that required manual assistance. eg, a 10" car needed a 50" radius to facilitate coupling and uncoupling. However, I use Protocraft couplers and have to manually assist switching jobs on 60" radius curves. YMMV.
Bottom line, the 1975 parameters seem reasonable, but have to be taken into consideration as to what your running (i.e., trust, but verify). And, you should be able to fit 6 tracks in 30" of width, but what you can do when they are loaded and the setback, can be determined by trial and error.