Hi Harold
A warm welcome to our great forum of Märklin fans
A short presentation of you (which region, which fields of interest, age occupation) is not mandatory but would help get acquainted.
Here a French crazy person (from Paris area) about Märklin HO digital, computer control of trains, Faller Car System

Not sure that I will answer your questions but lets try:
- space between levels: it includes the base board thickness (10mm) the C track height: 8 mm; clearance for trains 67 mm Clearance for catenary mast 97 mm.
- I selected 100 mm (of height between levels) and it turned out to be not enough (inconvenience of reaching a derailed train,, etc 120 mm is better.
- side clearance : straight or very wide curves 30 mm on each side of the track (C Track width is 40 mm meaning 20 mm on each side of the track center
- side clearance for curves: it depends on the radius (of course sorry) but also on extra long vehicles (Big Boy, Goliath crane, etc).
- so for R1, R2 and R3 77 mm track spacing is barely enough for "normal length" vehicles (cars under 300 mm in length). NOT any signal may be installed in the intertrack space
- for spacing between R3, R4 and R5 is 64.3 mm and this is barely enough for normal length vehicles (270 mm max)

Note: some Märklin items cannot be used "as is".
A curve followed by a counter curve is PROHIBITED with R1, tolerated with R2 and OK with wide radii

Some Examples of normal length vehicles (270 mm) that cannot be accomodated:
- a R1 curved bridge, because of the railings
- a level crossing because of its gates
- a 7286 turntable, because of its railings

I hope some of the above will help you
Jean

Hello there.

I just registered here. Notice that a small presentation is recommended. I registered here, because I have picked up my old starter set with steam loco 3000 and thought to build a small layout with metal track. I'll probably have to add some tracks to make it interesting, but that's another story. About myself I can also add that I live in Sweden, and I am close to retirement age.

Looked around a bit in the forum, and saw this topic. I think I actually have a 'rule of thumb', which I intend to take into account for my own part. Then I feel pretty safe.

Because there has been some previous thinking about this, and other things connected to model railways. Here is a link to 'Standards of European Model Railroads', by MOROP: https://www.morop.org/in...hp/en/nem-the-norms.html

Relevant to your (and my) considerations are the following standards:
NEM 102 Area Clearance on Straight Track, link: https://www.morop.org/im...102_en_2019_20231122.pdf
NEM 103 Clearance Perimeter in track curves, link: https://www.morop.org/im...NEM_E/nem103_en_2016.pdf
NEM 105 Tunnel Profiles for Normal Gauge Railroads, link: https://www.morop.org/im...105_en_2013_20170903.pdf
NEM 112 Track Spacing, link: https://www.morop.org/im...NEM_E/nem112_en_2016.pdf

There are also some other interesting standards, but those are topics for other threads.

The principle is that you start from the straight standard NEM 102. Then you add different measurements, if it is a tunnel, or a curve, and depending on the radius of the curve. There are tables for different scales.

You can simplify a little, and start from NEM 112 Track Spacing, and add the required space for the curves according to NEM 103 Clearance Perimeter in track curves.

The total height is probably quite easy to see in the NEM 102 plus height c-rail.

The width has to be calculated a bit:
Calculation example width (I hope I calculated correctly, correct me otherwise):
For passenger trains with long passenger cars (group C) on R3, we can calculate 46 mm + 2x11 mm = 68 mm wide tunnel for R3 radius 515 mm. It's of course also sufficient for R4 and R5. Narrower is sufficient, if the passenger carriages are somewhat shorter. For freight trains, for group A (freight wagons length max 230 mm) and for radius R1 360 mm, we have 46 mm + 2x8 mm = 62 mm wide tunnel.

Personally, I would certainly do some testing and have a little more margin. If there is a derailment, it can be nice. Where it's tight, calculations can be useful, for bridges e.g, which you don't want wider than necessary. As mentioned above, track spacing are excellent guidelines for tunnel widths.

A warning about NEM dimensions: It applies to models of prototypes that fit the German railway clearances.

There is equipment in real life that is a bit larger, like the 32 axle heavy load car or the US Big Boy.
The latter may need a few extra millimetres on the outside of curves, the former will need a few extra inches on the inside of curves.

Always test with the largest rolling stock you have.