How High the level?

[stuartmit]

I want to build a 5 x 11 layout that is a dogbone folded in a u, such that one of the loops at the end is located over top of the other end. This would involved climbing a grade, and locating the upper loop on a "mountain" above the lower loop which tunnels underneath. I have always heard you need a seperation of 41/2" in height or so between levels, But I  find that to accomodate tunnel portal heights you really need about 61/2 or 7" which makes the grade much steeper.  Any suggestions? I already have decided not to use gargraves track because I think the magnetraction is not as effective. How can I lower the height needed?  

[Yardgoat]

I agree with v8vega. You're best bet will be to make your own portals. The 4-1/2" figure is really a bare minumum for running conventional sized cars. If you plan to run scale sized cars, you'll have to jump that figure up to the 6" mark or so. I found I needed 6-1/2" clear (railhead to roof) to run scale double-stacks. That was too much for my layout, so the double-stacks will be liquidated for more conventional sized rolling stock.

If you're holding to the 4-1/2" clearance dimension, instead of a tunnel portal you can disguise the opening with something like a highway bridge that the train passes under and disappears into the mountain. Lots of other visual blocks could be used depending on your scenic desires.

Neil

[Buckeye Riveter]

Manufactured resin based tunnel portals can be shortened in height.  

[lionelsoni]

I think that the problem here is not so much that of reducing the portal height as of reducing the thickness of the lintel, without making it appear so slender as to be structurally useless.

I suggest putting the actual (grade separated) crossing inside the mountain.  The upper track can still be mostly exposed, but with its own short tunnel(s) where it needs to cross the lower track.  Then the height separation can be as little as the train height and track thickness require.  You can even remove ties from the short part of the upper track over the crossing, so that only the rail thickness (9/32 inch for O-27) matters.

[Buckeye Riveter]

I normally cut the two imposts to shorten the tunnel opening height and leave the abutment above the keystones intact.  I almost made this opening too short. Double stacks will not fit through this portal. 

[lionelsoni]

The problem with leaving the top of the portal intact is that its height (which looks like it might be a good 1 1/2 inches here) gets added to that of the opening if you locate the upper track at least as high as the portal top.  Locating the upper track behind the portal but lower than the portal top would look very strange.  That is why I suggested getting both tracks into tunnels inside the mountain before they cross, so that no one can see how little clearance they actually have.