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What is the acceptable percentage grade for most Lionel and Williams locos, and what length is necessary to obtain about a 5 1/2-6” clearance?  I’m new to 3R modeling and am considering adding a overhead track on the layout.  I understand train length and weight will limit grades, but generally what do most of you folks use as a standard.  I have about 10-12 feet to build the grade.

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Most people seem to recommend keeping grades at 2% or less.  The track planning software I use turns the percentage from green to yellow at like 2.5% and red at 4%.  To stay at 2% for a 6" clearance you'd need to run 300 inches or ~25 feet.  With 12' you'd be looking at a 4% grade to rise 6 inches.

FWIW, a lot of people here have recommended about 7" between tracks, but I think this is to leave room for the thickness of the benchwork supporting the track and/or a bridge.  If you are crossing over with just a bridge, don't run double stacks or high cubes, and your roadbed isn't that thick, you might get away with less.

Edit: I would add that I've seen people get away with up to 6% grades if they have traction tires and keep the trains short.  The other thing to look at is how much of the train will be on the grade at anyone time.  There are trade-offs to be made there between grade length and slope I'm sure.

Last edited by rplst8

I use a 6% grade. I run MTH with about a 10 car train length. Steam engines have less pulling power than the diesels. You have to be mindful of the steep grade on curves, as this can slow things down. If you go through 2 curves on a steep grade, the train may stall due to the added friction of the corners. On my layout, a 10 car train rarely is in two curves at the same time for very long.

@Joe K Thank you for your reply.  This is something that may also be an issue on my planned layout, curves in grades.  I know what you mean about the added friction in curves.

On your layout, what type of track do you have, what are the curve diameters and Arc degrees within the 6% grades?

Also do you have any single motor diesels that work with 10 cars on the 6% grades or are they dual motor units?

Last edited by SteveH

I use fastrack 048 and 060 curves on my 6% grades.

All but one of my MTH diesels are single motor engines. They all have traction tires and handle the grades well. I generally run between 15 and 20 smph on the grades.

Just a note, any underweight cars will tend to pull off the track (derail) at the curves if you have the train on two curves at the same time going up the grade. A great way to identify problem cars without weighing them.

Funny, testing car weights with curves, know what you mean.  Thanks for the answers. I use FasTrak too.

One more question, when I asked about the arc degree, another way to put that would be: each full curve section of O48 is 30 degrees and O60 is 22.5 degrees per piece.  So I'm trying to get an idea of how long the O48 and O60 curved sections are in the 6% grade.  Any chance you might have a SCARM file of your layout?

Last edited by SteveH

Here's the section of my plan that is questionable.  It's about 10' Long with mostly O60 and a few pieces of O72 and has a 6% grade rising 7".

V5a Sub out

Here's a link to the post with the full SCARM plan where I've asked about this yet to be answered question.  Any insight on the clockwise grade coming out of the Subterranian level would be greatly appreciated.

Appalachian Mountain River Town


Images (1)
  • V5a Sub out

Instead of making your overpass high, you can also depress the underpass. That way, both over and under can have relaxed grades and accomplish the same thing.

Real railroads sometimes increase tunnel clearance by digging out the ground under the tracks. It's cheaper than re-boring the tunnel walls and ceiling.

Another important factor: you can't start a grade at 6% without risking electrical and running problems regardless of whether or not curves are involved.  You have to include what are called vertical curves (I prefer to think of them as transitions) where you start from flat and start a gentle rise.  So, if you still expect of rise of say 5 inches in 10 feet, with two transitions of sufficient length at top and bottom, your ruling grade (the steepest point) might have to be 8% to 9%.  That is so much harder on engines, it's almost not worth doing.


Yep, the easement into and out of the grade for anything that has more than four closely spaced wheels will take up considerable space!  I have a 2.5% grade on my layout, and I had to use about five feet for easement into and out of the grade.  In my case, that was to allow big stuff to run, I have a lot of scale articulated locomotives like Challengers, Big Boys, Y6b, etc.  The goal was that they could run anywhere on the layout.

Last edited by gunrunnerjohn

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