My ideas

The ability to go either up or down is the challenging part.  As I see it, you have two options.  One is to build in two connections to the helix - one off the front which allows a train to go one way, and another half a turn higher off the back which allows the train to go the other way.  The other option would be to build two helixes, one going in either direction.  Access for the inner one would have to be via a crossover or diamond (I'd go with the diamond - no moving parts) on the outer helix.

Is there a better way to achieve the desired operating pattern?  This seems rather complicated to me.

3 levels and a helix....

Better Idea

Ken basically he is doing the line that goes through our home town, (Huntsville, Ontario) about 250 km north of Toronto.

The South Fork will have Martens, a large passing siding, and one industry(Domtar).

The North Fork will be the Huntsville Station and yard area as well as two industries, KWH Pipe and Limberly Clarke.

The upper level is staging and he want to have trains assembled to simulate coming north from Toronto or coming south from North Bay.

This is why the desire for the complex helix.

Staging in the middle?

I'm not sure if it would solve anything, but could you put the staging in the middle instead of on top?  that way there's only one way for a train to go from either the north or south districts.

Instead of a helix why not nolix

Instead of a helix in the 5 by 8 room, why not a nolix, this would give him some scenic area while the train gained elevation.  A nolix is a modified helix; in his room of 5 by 8 I would do an oval helix, with the facing front a rather nice slinky sex S curve.  Below is an image of my nolix in N scale in a smaller space.  Each level is different from the others, unlike a helix which is uniform all around.  

The picture is taken with a very wide angle lens so distortion which gives it a roller coaster effect visually but the grade is uniformly 2.2%  Only the second and third levels in the front snaking S curves will be visible; the first level is directly below the second and will be hidden by scenery.  And if you look at the fourth level, built on the other side of the "ribs" which will be the skeleton for my mountains, it will be totally hidden as well.  The backdrop is "peak a boo" only which you will only slightly see between the mountains.

Nolix

This sounds interesting.

We have already decided that for the necessary clearance and radius we will have to spill the helix out into the main room. Thus giving us more than 60" for the radius.

Thanks.

Two tracks

On another forum we got a possible solution to the operations.

Have a two track helix (or nolix as per rsn48's suggestion).

To explain:

Inner Track: From the south end of the staging track we enter the helix's inner track via a diamond, travel all the way down to level one. Exit and connect to the south end of the level.

Outer Track: From the north end of the staging track, we enter the helix's outer track, travel down to level two where we exit the helix. Entering the level from the north end. Travel around level two and re-enters the helix as the outer track, then proceeds down and exits on level one, connecting to the north end of the level.
 

Thus we have formed our complete circle for continuous running.

what problem?

I don't see why any sort of diamond or turnouts are needed to do what is required.  Build the whole thing double track and have the Toronto to South line go down the inner track from the top to the bottom. Then the outer track is used by the North Bay line to the upper deck, where it gets off to run around the North line around the room.  When it gets back to the helix, it gets back on a turn below where it got off and goes to the bottom deck.  It then heads around the room before meeting the line going all the way back up the inner track.  No problems.

Thank You Jurgen

I think you have hit on it. Your plan is simple and foolproof and will do it.

Thank you Jurgen.

Limits route possibilities

Route control

You are correct Larry, however, he wants to operate like the prototype through our area, so the linear route is his choice. He has already ordered some things off a fellow in California. He is getting the plans for an 8 foot diameter helix, the 16 uprights and wood for one revolution (so he can use it as a template) and for for only $1,000.00

Helix alternative

Depending on the length of the trains an alternative might be a train lift. This could be dual purpose with several tracks as a sort of vertical traverser as well as level changer. If the trains are short a paternoster system might be effective but long trains really require a straight lift to allow for several lifting points. However "straight" as used above does not limit the shape of the tracks and they could be curved to suit the location.

Small train lifts are available commercially but the massive layout in Germany has one that looks to be about 16ft long.

Archie

Helix vs. Track Switch

I have heard people say to keep track switches away from a helix.  But I see people using non-circular helix shapes, i.e. adding a straight side and then putting the track switch in the straight section.  But in my helix, I have the curved side of the track switch in the circle of the helix.  With proper engineering and construction, you need not fear using a track switch in a helix.

At this point, the discussion may have moved to a solution not needing track switches, but you never know if it might come back.

make 'em work hard to collide

I have built many helices, and our club has four so far, and another 6 are anticipated before the layout is done.  Our previous layout had one two track helix and one three track helix.  I would always make sure that there is no way for trains on different routes to hit each other.  This means, I would not put in a crossing or require trains on different routes to use turnouts such that they could collide if people aren't watching what they are doing.  In hidden track like a helix, separating routes is the only sensible way of doing things. Of course, they are your models, and you can take whatever risks you like with them.

It may interest you, though, that it is possible to have a train enter the inside track of a double track helix and emerge from it half way down without using a crossing or turnout to get past the outer track; it just takes a little more room to do it.  One of our helices does just this on our club layout.  (Unfortunately as I write this our server is down, so I can't link a photo of the beast.)