Distance needed between start of grade and turnouts - HO scale

Model Railroader Layouts and layout building
1

I’m building a large HO scale layout. What is the minimum distance needed between a turnout and beginning of a 2% grade? And conversely, coming down off the grade into the turnout? I will be running lash-ups of 2-3 locomotives- typically SD70s, with consists of 8 or 9 feet. Thanks in advance for your input! Locogirl

2

You can start the transition to the grade at the end of the turnout. The length of transition needed is determined by your longest individual piece of rolling stock, not the number of engines or length of train. Pretty much the shortest transition that will work is a longest car length for every 2% change of grade. Anything less, and you may have problems with accidental uncouplings due to coupler over- and under-rides. The exact amount of transition depends on both how much your cars and loco trucks can pitch up or down, and how well matched and high your coupler faces are. If you are going to use shorter than recommended transitions, I strongly recommend setting up a test section with your proposed grade and transition, and run your rolling stock on it to check how well it will do and what issues you may or may not have. Mocking up any likely difficult areas prior to committing on a large layout is always worth the time to me.

Back in the days of 1/2" or 3/4" plywood subroadbed, grade transitions were never an issue. The plywood would form a natural curve with a suitable transition to a grade. You couldn’t bend the plywood to a sharp enough curve to be too tight a transition. I would imagine cookie cutter foam instead of foam risers would result in the same natural transitions.

My opinion of foam risers - they are nothing more than the foam equivalent of the plastic over-under piers sold for use with train sets, with the same issues. Others think more highly of them.

Turnouts need to be in a flat plane, both across and length-wise. They can be on a grade - but it must be a constant throughout the turnout to give a flat plane. The flat plane for a turnout on a grade will give a slight positive or negative super-elevation to the curved branch, but should be no problems operationally unless the curved branch is very sharp. Just use a smooth transition to the curved branch.

my tho

3

Fred, Thank you. You confirmed what I suspected in regard to the longest piece of rolling stock. I will definitely build a mock-up, and avoid a potential headache. I was planning to use the subterrain foam risers, but may re-think that idea. Thanks also for your thoughts on turnouts being on a grade. I intend not to place them on a grade, but it’s nice to know I can if needed. Locogirl

4

Hi,

on my layout it is about 30 inches that I used to transition from the flat to a 2.2% grade. There have been no issues with derailments or cars uncoupling. Also this transition has been made by simply bending the plywood and supporting it with shims to prevent it from bending too fast. The more gradual the transition the better,

As for having turnouts on the grade, that is of no issue. As long as they are not it the transition area. I routinely push 10 freight cars up a 3% grade through a turn out. If the turnout is not defective then there should be no concern.

I too model in HO and run AC4400 and SD90/70/45/40’s.

Hope it helps

Frank

5

Hi!

I just finished the lower level of my 11x15 HO layout, with code 100 flextract. It has a 2 percent incline up to the main level. I did a lot of testing before I considered it “finished”, and one of the areas I had to adjust was the vertical transition (combined with a curve) into a # 6 turnout. I have high standards for track/wiring/benchwork, and zero derailments was my goal. My most demanding test locos are a BLI 2-10-2 & 2-10-4.

I had a couple of problem areas around the turnouts, and the “mechanical” ones dealt with:

  • a curve led into a turnout without a smooth transition (minor kink in other words). I moved the turnout so as to allow about 8 inches of tangent track smoothly flowing into the turnout.

  • a vertical transition flowed into a relatively level turnout. While this looked really smooth, the long drivered locos didn’t like it much. So, I again moved a turnout to allow about 8 inches of trackage that was level with the turnout.

One thing that I “relearned” was that you really need to eyeball each of the tracks leading in/out of a turnout for smoothness - not just horizontal, but also vertical.

Hope that helps!

Mobilman44