Article by Scott Watkins
As I've built and modified layouts, I've come up with some general rules to follow that keep me out of trouble. These are pretty basic and can be utilized with any model scale you are working with. These basic rules can be generalized to fit your choice of scales.
I recommend you start by selecting the scale for your model trains and layout (I told you this was basic stuff!). The next step is to estimate the amount of space you have to fit your layout in. Take some measurements, make some estimates, and leave room for "error.". Sketch out your ideas on paper to give yourself a sense of what is going to work in the space you've allotted for yourselfEstablish the smallest dimensions you can use in your layout for grades, turnout angles and curves. This is all dependent on the locomotives and rolling stock you are using. Short trains can get away with smaller radii on curves and turnouts, and longer locomotives and rolling stock will need the longer radius curves, up to 30" for HO scale.
Prototype railroads have a maximum grade of 3%, however, if you are willing to "cheat" a little you may be able to go to 4% or even 5%, if you are using powerful locomotives and/or shorter consists. For tracks that cross over each other, you'll need to determine the proper rise for your scale. Remember to factor in ballast height, load heights, etc.
Minimum Clearances For Your Layout
When tracks are running next to each other, you must verify the clearances. You don't want two trains to bump into each other, causing derailments! The turns are particularly tricky - the best way to confirm your minimums is set up two sections of curve and set your longest locomotives along them, and note how far the ends of the cars overhang the track, and how far the middle of the car is over the inside of the track.
Layout Drawing Tips
I begin by drawing the outside measurements of the space I am working with, including any fixed obstructions (like posts). This could be the size of a table top, a four by eight sheet of plywood, a shelf, or the inside dimensions of a room.
Then I sketch major scenery (rivers, roads, towns, farmsteads, etc. When I am trying to re-create a real place, I work from maps, or measurements if available them from a scouting visit (model railroaders have excuses to travel to some pretty interesting places!)
Then I draw in the major corners of my tracks I know which turns are going to have ninety degrees, so I'll draw a circle there using the radius I need. I draw circular arcs at all the corners. I then connect these arcs with straight lines or broad curves to fill in my tracks.
At this point, I'll locate sidings and switching yards. Try placing these in a variety of locations. Use your imagination and visualize as much as you can. This is where using pencil, or a computer CAD program for track layouts comes in handy.
I then make a three dimensional elevation drawing to check heights. You'll find this very helpful, especially if you have elevation changes or track crossovers. Set an "origin point" at the lowest part of the layout, and measure up from there.
Construction Phase of Your Model Train Layout
You can make a full size layout drawing and lay out your track right on top of it, or trace through it to your bench top. If you don't have a plotter that can print the full layout on a single sheet of paper (like most of us), then tape together the smaller pieces of paper, making sure to measure across several sheets to ensure you are keeping it to scale.
Another good idea is to mark your co-ordinate system right on the bench. Make an X and Y axis, perhaps along a wall or two, and then draw in your layout. You can then take the co-ordinates of major features from your scale drawing and place them at the same co-ordinates on the bench.
As you build, check by placing track, buildings and other features on the partial layout. Make any necessary adjustments as you go. This is the fun part - building your layout. Take time to operate your trains through you layout, using your imagination to fill in the gaps!