Woodman, I'd have to agree with Mike's reply. Some just like to see it. I laid out my track because I felt like you. It just seemed so tight. And to make matters worse, I am modeling in N-scale in which the parameters were even smaller. And then the thought of a double double main going into a mountain on a curve seemed even harder. Now I noticed you said you will not be running any over sized cars, but for me, I took some liners .. just to see the actual clearance. But like Mike suggested, just lay them out, and see what you've got. Some just like to see it.
Two inch track spacing measured from center to center.
Elmer.
The above is my opinion, from an active and experienced Model Railroader in N scale and HO since 1961.
(Modeling Freelance, Eastern US, HO scale, in 1962, with NCE DCC for locomotive control and a stand alone LocoNet for block detection and signals.) http://waynes-trains.com/ at home, and N scale at the Club.
For straight double track , 2" track centers allows adequate clearance. You may be able to go to a max of 2 1/4- 2 1/2", But as mentioned do test w/ track/ roadbed if you plan to go wider.
This spacing of 2 1/2" @ the bridge, narrows to 2 1/4" @ this portal
However this portal placed on a radius and using 2 1/2" track centers, the portal will need to be widened. This thread explains this http://cs.trains.com/mrr/f/11/t/216329.aspx Selector cut and added a section, I decided to use 2 portals to accomplish this
Modeling B&O- Chessie Bob K. www.ssmrc.org
Maybe you could set a couple of pieces of track side by side, with a car on each track, and see what spacing fits the portals.
Mike.
My You Tube
I purchased 4 Woodland Scenics double track tunnel portals. I will have 2 sections on my layout where I will have double tracks entering tunnels. What should be the spacing of the tracks when they enter the tunnel. The opening measurements for portals are 4 5/8" wide, 3 13/16" high. When I look at the portals it looks like it will be too tight entering the tunnel with the double track. I am modeling in HO scale and will not be wunning any over sized cars.