Clearance Dilemma

Here's something simple that would improve clearance.

There is a short aqua straight track section (looks like about 6 inches in length) at the lower end of your aqua S-curve that leads onto the bridge. Remove that aqua section to move the entire aqua S-curve downwards in your diagram and insert that same straight aqua section at the top of the aqua S-curve. Similarly, on the yellow S-curve, remove the short yellow straight track section at the top of your diagram and put it at the bottom of the yellow S-curve leading onto the bridge. Those changes will move the two S-curves further apart and will increase the clearance. Lay the tracks and check the actual clearance with locomotives and cars before you finalize the track locations.

MELGAR

Thanks, I’ll try that.

You want to get away from sharp curves close to the straight track.  Maybe something like this. Don't know how much room you have, but the broader the curve the better.

Dave, you've helped so many with your SCARM skills, I'm not sure that I have anything to add.  The only thing that I can think of is some kind of reverse easement with flex-track, where the curve radius starts at O72, but gets really broad (i.e., almost tangent) as the tracks gradually blend together until they get within 5" of each other.  Scale articulateds are demanding beasts.  Good luck, please post back and let us know what you came up with!

Ron, thanks. That’s pretty much the way I had it, but this is the area I’m worried about with a large engine meeting another from the opposite direction. This isn’t for me, so I guess he’ll just have to set it to see.

Dave,

I'm not sure what track system you are using, but since the bridge is 40" with 4.5" spacing I used AtlasO track.

After the first curve it's 5.45" and after the second curve section it is 6" for the rest of the way.  You can extend the diagonal section to get to the width.  You can reduce the parallel curve section diameter equally (must maintain the 4.5" radii difference) on either or both ends.  The reduction does not have to be the same.

You can increase the straight track coming off the bridge equally if you have clearance problems.

Jan

Thanks, Jan. I guess I was thinking that the 1 engine with the overhang going toward the track next to it would hit, but the other train’s overhang would be to the other side, so it seems that might not be the case. BTW, the tracks are Atlas and the curves O-108 and O-99.

Ted, thanks for the kind words. Looks like Jan had the same idea, so I think that’s what I’ll go with until it’s time to  test.

I battled this same issue a couple times, having to send out the surveyors and blasting crew to realign track.  I drew and measured, made templates and the only thing I found was fool proof, was to put it all together on the floor.  I laid out brown paper, put the track on it, and ran the two locos that would interfere, moving things around until I knew nothing would hit, and the transition from straight to curve can be an eye opener, not at the pilot, but at the back of the cab.  When I was happy, I used a Sharpie and marked the brown paper for track position, cut it out and used that as a template at the final location.

I would think that with O-108 and O-99, 4.5” would be adequate even with a Big Boy.  Is this 2-rail?

No, Ron, it’s Atlas 3-rail. I’ve always read that modelers go with 6" for the larger engines, even with large curves. I’ve always thought that was overkill, but it might have been more about visual appeal than concern about hitting. From what I’ve read, the generally used clearances are 3-3.5" in yards, 4.5" on straight runs and 6" on curves for the larger engines. The builder is a novice, so I’m probably being overly cautious myself. He’ll lay it out before he tacks things down and it’ll be some time before he gets to that point. There is room on the decking to move things around a bit, so I’m just trying to make things easy for him.

@DoubleDAZ posted:

Hi All,

I've got a problem trying to go from a 6" of clearance between dual main tracks down to 4.5" to cross a dual track bridge. Here's what I've got so far, but I'm concerned that large trains (Big Boy size) going in opposite directions will hit. Thanks for any ideas.

Dave- Is it possible to move the yellow track higher up on the plan? Not sure what's happening past the clipped section at the top.

I think your best bet it to get the tracks parallel well before entering the bridge to avoid overhang issues.

I agree that this may need to be mocked up and tested.

Bob

@DoubleDAZ

I echo @RSJB18 the curves are to tight before the bridge. A gradual angle in would be much better. Is it possible to move the yellow track further away at the top and then come in more gradually towards the bridge. Not knowing what’s at the bottom of the picture; the blue track has to start much earlier to move towards the yellow. Again as an angle instead of a curve.

Bob and Bob, I’m going to go with Ron’s suggestion. That’s close to the way I had it before I started overthinking things and made the overhang worse with the curves. I might try flex track for a smooth transition from 6" to 4.5". There is room up above , so the curves don’t have to be concentric. There’s actually 3 tracks, but the 3rd is further away on a single bridge. There are straight sections, maybe 12-15", so the gold and blue tracks can be moved up and can come down at an angle instead of looping around that nook leaving room for landscaping in the corner.

Dave,

I run 4.5 inches center rail to center rail on my layout on a long grade, where there appears to be a double main.   

Inside diameter of 096, radius = 48 inches.   Outside of the curves is obviously 52.5 inch radius.   I have a total of 360 degrees of turn on a 1.5% grade set up like this that's how I get the folded over dog bone done on my 240 foot main line.   

I run 2 large  articulated O scale steamers,  3rd Rail Sunset Allegheny 2-6-6-6,  Lionel B&OEM-1 2-8-8-4, and I also run 21 inch passenger cars, the Atlas O California Zephyr cars and Sunset/3rd rail brass Heavyweight pullmans.

It runs perfect, never had an issue.  Obviously, I did exhaustive mock ups before I went through the effort to build the 1.5% grade and lay all the track.

Also Yes I did easement transitions at the entrance and exits of all these curves.   It's essentially a 90, then a large sweeping 180 than another 90 to get to the top of the grade, or the bottom depending on which way you're heading

@chris a posted:

I run 4.5 inches center rail to center rail on my layout on a long grade, where there appears to be a double main. 

Chris, the acid test might be the Lionel Rocket Booster train.  It has wider cars, and after building my layout and running every large articulated locomotive I had, I had an inside curve clearance issue with the rocket booster train!  The clearance car is 3 3/4" wide, SURPRISE!

You could eliminate the dual bridge and go with two single bridges to enable you the open up the distance between the two tracks.

Rod, if it were my layout, I might, but then I’d probably do a lot of things differently, like shrink the curves to O-99 or even O-90, though then I’d probably have to use O-81 and O-72 for some concentric triple mainline curves. I’ll have to see if the bridge has already been bought. There’s really no reason it has to be across the entry. This is an around the room style layout with 3 walls and the one leg goes down, in and down again from the top wall to the bottom wall. There’s also a dead end extension where I’ve placed a RH, TT and yard.  Part of the problem is there’s no theme, so it’s just laying tracks to see what he likes. But, if I can have 4.5" clearance all around, I can go back to my original design that was like Aron’s.. I think he only has 2 large engines, the Big Boy being the largest.

Okay, here's what I've come up with. I moved the bridge down a bit to make the blue straight on top a little longer. I used flex track in 3 places; gold below the bridge, blue above the bridge and just before the purple. I may try to recreate them with cut sectional curves, but I think I can talk the builder into using the flex. I also included more of the space in the photo so you can see what's available. This part of the bench work is open on the sides while the top and bottom are along walls. There are other things not shown in the photo dictating the configuration. As always, thanks for your suggestions.

Looks good Dave. A little thinking out loud helps sometimes.

Bob

It certainly does, Bob. And 12 years of help on this forum is worth the price of admission.

Looks like a great solution Dave! Nice work!

@DoubleDAZ posted:

Ron, thanks. That’s pretty much the way I had it, but this is the area I’m worried about with a large engine meeting another from the opposite direction. This isn’t for me, so I guess he’ll just have to set it to see.

You'd be fine with this solution. The issue is not 2 large engines, but an articulated locomotive on the inside and a 21" passenger car or an auto rack on the outside. You're ok because the long car is still going pretty straight at the point where the locomotive on the inside is coming off the turn. Ive built and tested "all same size" curves on parallel tracks for a modular club and everything clears. It was tested with a C&O turbine and scale size auto racks (about as much as you can hang off of everywhere), no issues.  You offset the curve starts by the track spacing between... so add 4.5" of straight to the outer track. You get a spacing close to 6" in the center of the curves.  To end up with 6" on the other side probably need to add a bit more straight to the opposite side (where the spacing is 4.5").

For the other side of the bridge, instead of a fraction of an O72, use a fraction of a much larger diameter (99, 108, etc), or bend a piece of flex track to fit.