VOTE NOW. (If you need more layout info let me know)
What real railroad situation are you trying to simulate? That should determine what to do. In some ways double track main lines are pretty boring to operate.
Yes 2 trains wouldn’t be exciting after a while. It’s a moderate traffic RR (Class 2 actually) I do like the look of a single track snaking through a heavily wooded area. ST would also eliminate those 18" curves.
Single track with passing sidings give you more operational challenges.
Yes. But if i want siding(s) that can hold an entire train there will only be one long siding. i could sure run longer trains w/ 22" curves.
I voted double track but it is up to you. Im in N scale so the size of your layout seems massive for N scale until I realized you were modelling HO. So I personnaly prefer the look of double-track but to save space and $$$ I would go single-track.
Both, Run some single into a LONG stretch of double. This was what I SHOULD have done BUT went with a LOT of single and a little double or looks. Space was not my problem. Phase 2 will have the double and quad track mains.
Take Care
You hit the nail on the head. Generally speaking, double track is better for small layouts because it allows you to keep your trains running. Otherwise it will be stop-and-go traffic. Single track works well for larger layouts because there is a better ratio of running time to waiting time and you have multiple locations for meets and passes.
If you are into operational challenges though, you can have sidings shorter than your longest trains. Meets are made through a switching technique known as a saw-by in which one or both trains is split in two and half the train takes the siding at a time. John Armstrong explains how this works in Track Planning for Realistic Operations much better than I can. It covers a variety of meets and passes.
I voted for double-track. My BRVRR is only 4’ x 10’ and is double tracked. Even John Armstrong recommended double track for small layouts. My outer main is 22 1/2" radius and the inner main is 20" radius. I can run up to 4-trains at a time, but usually limit myself to 2 or 3.
In the end, the choice is yours. Good luck!
i put single because most likely a class 2 railroad wouldn’t have the traffic to warrant a second. just my thougts
andrew
With single track you have a wider minimum radius and can better simulate the wide open spaces of a granger branch in the wheat belt.
With double track you can have one train orbiting the layout while you operate on the other main.
Most prototype lines single-tracked when CTC came in. Now the prosperous ones are relaying those second tracks if they haven’t already done so. (A couple of the coal lines out of the Powder River Basin are now triple tracked!)
I can’t speak for everyone, but the heavy-traffic railroad on my layout will end up with a single stretch of single track - because the prototype I’m more or less following was single track along there. The short line is single track with passing sidings because the engineering for double track would have broken the corporate bank! (The single track almost did.)
Single track, it offers a greater operating challenge.
Happy MRRing 
This page http://www.vetmed.auburn.edu/~smithbf/BFSpages/LDSIGprimer/Spaghetti.html has a description and drawing of a horizontal helix. If you can add about a foot along one side, you could have double track and point to point.
Enjoy
Paul
I would double track or at least make one long siding to hold a reasonable length train. The best would be if you could add even a 6" strip to the 4’ side of your benchwork so a larger radius curve could be used. 18" is really too restrictive for even a single track main. Just my [2c] J.R.
thanks. i’m looking at that now. I still can’t decide. here’s the pros. and cons. of each
ST- pros.- 22" mainline curves, would take less track, look less crowded
ST cons. only 1 train runs at once, have to tear out entire mainline to move it over a little
DT pros.- one train can run on the outside while i switch industries and yards via the inside track, 2 trains can run in opposite directions, would look very busy
DT cons. - curves on the inside have to be 18" while outside curves are 22", would need more track
I’m undecided. Here’s more about my RR. Freelance illinois central set in the present. It’s Class 2(for now). Primarily hauls Grain and truck trailers (intermodal) I Am willing to tear up the mainline to move it. It would look better w/ ST but i STILL don’t know (Jeez, can’t this guy make a decision?) BRAINSTORM!- have it be ST w/ an inside track next to the yard (aka. passing siding) so i can switch the yard while a train runs. But then again 2 long trains running would look cool. I AM going to have a 4- track staging yard when i add on (more about that later) Right now i’m leaning to ST w/ a siding for switching the yard.
inverted 8, that way the train crosses over it self, but ends up on the same track, I quite like it.
That’s my plan. I don’t have room for double tracks but I can run two main lines parallel to each other[%-)] Yeah I know what you’re thinking. I’m running two lines, one’s a dogbone and the other will be around the outer perimeter.
Fergie
I wouldn’t limit myself to either 18" or 22" curves. I know that’s what you are limited to with sectional track but if you go with flex track for your inside curves, you can make them whatever radius you want. A 4" separation between mainlines would look unprototypical. That’s 29 scale feet. Even with tight curves, you can probably get by with 19.5" radius for the inside track. That would be closer to what a prototype would run and would look much better.
Double track, because I think trains meeting at speed look, neat, cool, great, whatever. Good luck. Phil
There is NO WAY to avoid 18" inside curves w/ DT. The outside may be only 20" i just used 22" as the MOST i have room for.
That’s whhat i’m leaning towards.
will i ever decide?