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So there I was looking at the layout plan, and wondering if my larger locomotives and freight cars would really be able to safely pass one another on the curves with the proposed four and one half inch center to center spacing.  Another issue was would the three inch spacing from walls to the center rail work on the outer curves.  It was time to use my test loops: three concentric loops of Atlas track.  The loops, progressing inward, had O-72, O-63 and O-54 curves on each corner.  On one corner, the O-72 and O-63 had been replaced with O-81 and O-72 respectively.  On a second corner the outer curves had been changed to O-99 and O-90.  Spacing between center rails was four and one half inches.

For the first test, the Lionel UP Vision Challenger slowly pulled my standard test consist (which includes an Atlas Articulated Auto Carrier, a MTH Schnabel car, a postwar Lionel 6418 machinery car and Vision tank cars on the outer loop past the Lionel Vision Clinchfield Challenger halted midway through the O-72 curve.  While the Challengers passed one another with reasonable clearance, the forward portion of the Clinchfield Challenger walkway came within a quarter of an inch or so of the side of the auto carrier and almost as close to the Schnabel load.  The clearance was also close, but passable, for the ladders on the Vision tank cars.

The next test had a Lionel Legacy Big Boy on the O-72 curve.  The Challenger slipped by, but there was an interference fit (negative clearance) with the auto carrier.

I next parked the Big Boy on the O-90 curve and tried to run the test by on the O-99 curve, with the same results.  The Schnabel was also confirmed as a no go.

A bit concerned, I replaced the O-99 and O-90 curves with O-108 and O-99 respectively and re ran the test; no problems!

The final passing test had the Big Boy on the O-72 curve and a Lionel DD35A (alone) on the O-81 curve; again, no issues!

To check the wall clearance, I placed a cardboard box three inches from the center rail coming out of the O-81 curve and ran all of the locomotives through the curve; close but no issues were observed.

I hope that this is helpful for some of you.  It is nice to know that if my layout ever gets completed, trains will not be banging into one another or the walls (if the track is laid according to the plan).

First two photos are auto carrier passing Challenger during first test. Next is Challenger passing Challenger.  Finally, tank car passing Big Boy.

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Ted, interesting information in the referenced thread.  I wish that I had it before I did the layout design.  It’s a bit late now. So I’ just trying to determine what can be done with the pretty much cast in concrete plan (with four and one half spacing).

Russell, one point I should note is that all of the pictures in my first posting were taken with the trains on the O-81 and O-72 tracks.  My plan is to run the larger locomotives and cars on the O-108 and O-99 concentric curves.  I was checking to see if it was feasible to stick with Atlas’s four and one half inch spacing.  However,  your reply prompted me to do some additional testing.  The new tests were conducted with the Big Boy midway through the O-99 curve and additional freight and passenger cars and locomotives run on the O-108 curve.

During these tests, the Big Boy boiler was nudged as far into the curve as it could go.  The only close problems occurred with the 21 inch K-Line Amtrak passenger car, Weaver’s Bradley NH passenger car and the Atlas 89’ 4” flat car.  The clearance with the K-Line 21” car was very tight; the Weaver Bradley a tad better, but still close.  The Atlas flat without load was a no problem, especially because the Big Boy running boards are well above the flatcar deck.  Loads on the flat car made it more interesting.  With an Atlas trailer on the flat, clearance was close, but adequate.  The issue arose if the flatcar load extended beyond the edge of the flatcar, such as the missile launcher on the USMC tracked vehicle.  There was plenty of clearance with Lionel 18” streamliner and scale proportioned heavyweight passenger cars.

The Lionel ATSF 2-10-10-2 and 2-8-8-4 AC-9 Yellowstone steamers passed by easily.  I checked a Lionel AC6000, without issue.  The clearance distance is aided by the fact that most diesel cabs are well away from the middle of the engine, and the walkways provide extra spacing (the diesel’s handrails are below the Big Boy’s running boards).  A Lionel JLC GG-1 had plenty of clearance.  The only locomotives which could be problematic are the middle unit on the MTH Coal Turbine and a MTH or Lionel Centipede (none of which have walkways).

My conclusions are that, other than 21” passenger cars, Atlas flats with wide loads, Atlas articulated auto carriers, MTH Coal Turbines, Centipedes and Big Boys, locomotives, passenger and freight cars should be able to pass a Big Boy safely on O-99 and O-108 concentric curves.  I would note that you have to be sure that you do not undershoot the four and one half inch center to center spacing.

All of the attached pictures were taken with the Big Boy on the O-99 curve and the other pieces on the O-108 curve:

Big Boy and Articulated Automobile Carrier, USMC tracked vehicle missile launcher too wide, Dinky Toy 10-Ton Truck on Atlas 89' 4" flat, Big Boy and Atlas trailer on Atlas 89" 4' flat, DD35A passing Big Boy, Big Boy and K-Line 21' passenger car and Beaver Bradley NH passenger car and Big Boy

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This has been a very informative thread as was the link to the Layout Page in which Dave H. recommended 6" distance center rail to center rail.  I now realize I need some advice.  I am building my first layout.  It is 11' x 30'.  I am using Ross track.  I have a 2 track main that goes around the room.  In 3 of the 4 corners of the room the main lines have greater than 6" between them, but I have one corner that I am concerned about.

 

The two main lines cross over on a RCS 175 Double Crossover.  When the tracks leave the cross over they run parallel for 2' before they begin to curve.  I used O80 on the inside and O72 on the outside, which is fine until the end of the curve when both lines go into their respective straights.

 

It makes the most sense to put the large diameter curve on the inside (thereby reducing overhang)...right?

 

How can I increase the distance between the tracks at the end of the curves/start of the straights?

 

Any tips or advice would be much appreciated.

 

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The two parallel tracks at the bottom of the page are 4" apart center to center rail.  These tracks run the length of the room behind the walls on both long sides (30') of the room.  My train room is in the loft above my garage.  I have complete access, albeit tight, to these tracks due to the pitch of the roof.  They "return" to the train room at different points, so keeping 6" between them at all other locations is not a problem.

 

thanks for the inquiry

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