Track bed

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NP2626

Active Member
#1
Where I live, in Minnesota, demonstrates that our model track bed is not deep enough. I used Midwest's Cork Roadbed under my track and while this basically covers the ballasted portion of the roadbed, Most of the time real railroad roadbed is much thicker. I drive by the old Northern Pacific tracks (now BNSF tracks) regularly. The prepared road bed for this section of track was prepared back in the 1800s and the road bed is much thicker than just the ballast! This would be a good place for a manufacturer to come up with a foam road bed for our models to make our road bead more realistic. Something about 1 inch thick would be a great addition to track laying.
 

NP2626

Active Member
#3
There are plenty of places where 7 feet high would be right and in fact, I would rather have more than I need and cut away that which I don't.
 
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Selector

Active Member
#4
No, I'm afraid you are quite wrong, Mark. The typical groomed ballast height is between 18 and 24". Piling 7' of ballast would require the railroads to mine and locate up to a ton more rock per linear foot of ties and rails. Think about it; you would have to factor in the natural and engineered angle of repose of that much crushed rock piled up to 7' high. How much rock would have to fit under each linear foot at the 30-40 degree angle of repose that would withstand the lateral forces on the ties and rails along curves?

That would add millions of dollars to their operating budgets, but it would also be completely unnecessary.
 

Rico

BN Modeller
#5
We used machinery to drag up earth and clay for subroadbed which formed the ditches.
This would be graded and packed with pit run, then ties laid on top.
Ballast was added after track was down then tamped down.
In lower areas more earth would added to bring the track up to grade.
To model this I think you could lay the Midwest cork on top of sheet cork, or for lower areas styrofoam strips.
Mark, I've seen track with twenty feet of subroadbed here on the prairies!
 
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tootnkumin

Well-Known Member
Staff member
#6
Most of us would just form such banks out of plaster or whatever scenery base being used elsewhere. That's where the plywood cookie cutter method or foam sub-roadbed has the advantage over just a flat ply surface.
 

Selector

Active Member
#7
I was wrong, Mark....sorry. I reread your post and now see that you meant the roadbed, and not the ballast. Yes, the roadbed can be quite thick in a few places, but it would rarely be thicker than a couple of feet. Instead, the sub-roadbed, or fill if you prefer, can be as deep as many meters. The railroads that got tired of rebuilding torn away or burnt trestles eventually just trucked (by rail) thousands of cubic meters of rock and gravel, graded it, built up the roadbed to meet grade, and then laid their ballast to groom it.

Again, I'm sorry for not reading your post accurately.
 

wombat457

Well-Known Member
Staff member
#8
The cork or foam commercial roadbed is only supposed to replicate the ballasted portion of the track work and provide a shape for it. How high that roadbed is above ground level will depend on the hieght of the sub roadbed, and that can be any hieght you choose to make it using whatever materials that you have available.

Essentially, commercial roadbed is made to a fixed dimension that is (apparently) standard for roadbeds, generally speaking. Sub roadbeds, on the other hand, can be of any depth/hieght and or width; therefore, not something that would be practical for commercial manufacturing.
 
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tootnkumin

Well-Known Member
Staff member
#9
Harking back to your original post Mark, and the 1" thickness you used as the example, this is where foamboard would be ideal as it comes in several thicknesses, carves with a sharp knife easily to the angle you would want for an embankment (US might use a different name for that). At the current time, there is an inland rail line being built between Melbourne in Victoria and Brisbane in Queensland. It will also pass through New South Wales and controversially, cross a very flood prone area that has no natural drainage. It is intended to build an embankment 8' or more high over that plain, with culverts to allow flood water to pass either way, till it either soaks away or evaporates.
 

NP2626

Active Member
#11
This part of my layout building has been complete for 25 years, or so, and no, I'm not going to tear it up and start over. The posting of this thread was simply an observation of what is reality at least here in Minnesota and places West and East, that I have observed. I did use the Cookie Cutter Method and in some places my road bead is much thicker than just the Midwest Cork road bed. Like Rico said, this portion of the road bed is made up from earth from the general vicinity of where the road bed is going to be located. Much of it comes from Cut and Fill and the ditching used to channel water away from the track. The reality is also that the seven foot thick road bed is maybe close to average. I am saying that this feature seems not to be reproduced very much by Model Railroaders! Watch the photos, rolling by above, and see if you see any photos showing more than the cork road bed in depth and I know that I did not pay enough attention to this, when I built my layout!
 

NP2626

Active Member
#12
The parts of Minnesota that I live and often drive by, are what would be considered mostly flat lands. There are Terminal Moraines, where the glaciers piled dirt and rocks several hundred feet high when they ended their advances across the landscape; but, for the most part this is considered flat lands. Between here and the twin cities, there is maybe one Moraine that I pass over and about 1/2 the way to the cities, Highway 10 runs along side the Mississippi River Valley, crossing it a few times. During all of this length of run on Highway 10, the flat lands are still undulating low lands and shallow river banks to cross.

I guess what I am getting at is the large expanses of totally flat areas I see on my own layout and others, does not exist in reality and that the land always undulates and the track bed for the most part is made up of cut's and fills. In a 1000 foot stretch of track bed the track may go from 10 feet below grade to short stretches of being 20 and even 30 feet above grade, so a 1 inch tall piece of foam road bed would be more realistic than the flat expanses we see in model railroading!

This is not an admonishment that we need to do better at our modeling! It is only that I have noticed that reality is probably different than what we model and along with selective compression, there are other aspects to what we give up to make our layouts easier to build..
 
#13
Such undulating terrain can be simulated in a number of ways, while the track is dead level. In the case of a "cut", the terrain around the track can be built up using any number of techniques, from plaster-over-screenwire to plaster cloth over woven cardboard, etc. For "fills" the under-roadbed can be cut away, and a bridge, trestle, etc., used to span the gap. We do have to utilize selective compression to compensate for space limitations. A scale mile of track is approximately 61 actual feet. How many of us have space for even a scale mile of track?
 

bob

Administrator
Staff member
#14
Here's what the BNSF Industry Track Standards require for ballast. They want a drainage ditch on each side that's at least 1 foot deep. On top of the subgrade, you place a minimum of 6 inches of subballast, which is 3" minus rock. On top of that, you place a minimum of 6" of rock under the ties (in practice it's 6 to 8 inches). So, the cork roadbed should be about a foot thick, if not more. The total depth of ballast will be 12 to 14 inches (or more) when you include the ties.

As the original poster pointed out, this doesn't allow for the grade work, which is rarely if ever level with the top of the ground. At a minimum you'll have 1 foot below the bottom of ballast, and in many instances more. Keep in mind this is the rule for new construction, and you'll find all kind of stuff on existing track, especially old track. It's not uncommon for industry track in urban areas to be flat with the ground, sometimes the rails are buried in dirt, and there's no drainage to be seen anywhere.

As usual, it can be helpful to work from photos for inspiration, whether that's of an actual scene you're trying to model, or simply a location that you like and are trying to capture the flavor of.
 



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