Model RR toolkit - Compression

Model railroad = Shrinking the prototype?

Faithfully recreating a prototype stretch of railroad takes lots of space, even in N Scale.

To illustrate this consider a route known to many, the popular Tehachapi route in southern California. The line twists and turns for 58 miles between Bakersfield and Mojave. Reproduced in N Scale, this would require 58 x 33 = 1914 feet of linear benchwork.

Lets say you come up with a really efficient design with the layout on both sides of each aisle, and that your aisle is 3 feet wide. This translates to 1914/2 = 957 feet of aisle. If the benchwork is, say, 18” wide on average, each foot of aisle way requires 1.5+3+1.5 = 6 square feet.

So the bare minimum of space required to model this high density line is 957 x 6 = 5742 square feet. In other words, a room 100 feet long and 57 feet wide!! And that’s when you design it for a small footprint!

Smaller than 1:1, but how much smaller?

Unless you have 24/7 to run your layout, you really want it to be a lot smaller than just scale size. Why? Because an exact replica of the line in N scale takes the same amount of time to cover as the real thing.

On a good day, with no meets with other trains, a freight might average 20 miles per hour from Bakersfield to Mojave. The distance of 58 miles would take 3 hours to cover and much longer if there are encounters with other trains!! Most of us would want to get a train over our main line in somewhat less than that.

So the sweet spot for compression lies somewhere between a highly compressed 2 x 4 coffee table layout and a faithful scale replica. Since we have usually scoped out the maximum amount of layout space we can lay our hands on, the question is really more about what parts do I want to model and how should I compress them so they fit in my available space.

Non-linear compression

One approach might be to compress everything to make it fit. Instead of 58 miles, make the line, say, 50 times shorter, or 1.16 actual miles (38 feet in N Scale). The problem with this approach is that everything is now 50 times smaller. Sidings that are 5000 feet long on the prototype are now 100 N Scale feet long on your layout - that’s about 8 inches long. And that awesome looking 100-car coal train needs to be shrunk 50 times too. Of course it really loses something going from 100 to 2 cars long!

Rather than compress everything the same amount until it fits, we tend to produce a list of the ‘essential parts’ of the line we wish to model - a junction here, a funky bridge there, this station, that yard, this grade crossing, that industry, and so on. Everything in between is then be dramatically squished and becomes generic looking track, landscape and buildings. After all, these are the parts we left out, and its main job is to keep the essential parts separated.

The essential parts are usually still too big to model 1:1 in scale so we shrink them to make them fit our space. For example, the 5000 foot siding might reduce down to 2500 scale feet (about 17 real feet in N scale). Shorter than the prototype, but long enough to hold a 35-car train comfortably which is still a decent length train depending on what you’re trying to replicate.

Varying the compression of your line is called non-linear compression and it is a really important concept. It’s a key sleight of hand that underlies the ‘wow’ factor of model railroading. Because your brain responds as if the whole layout uses the same (linear) compression, and since your brain builds a scaffold from things it recognizes, it in effect just takes the compression factor you have used for the essential parts you’ve modelled, and applies that factor to the whole layout. As long as it is not exposed to anything that draws attention to the compression, your brain is pretty content to accept what it is seeing. The layout seems bigger because it grants you the benefit of the doubt on the ‘filler’ pieces, by seeing it at a lower compression than they really are.

Competing against the illusion is anything that your brain recognizes as ‘wrong’ in the compression equation. For example, this might come from being able to see two scenes at the same time that are, in reality, miles apart. The brain can’t always ignore such facts and if so, the illusion suffers. The layout still simulates some of the sensations of watching trains pass by, but the effect is less.

Note that as far as compression is concerned, ignorance is bliss. The less you know about your prototype, the less likely your brain is to jolt on something and declare, hey, that’s not right! Of course, others who know more about your prototype are likely to experience the illusion reduction, which you may or may not care about!

What to include and at what compression?

Because we usually model a line, the essential parts end up strung together, usually in the same order and geometry as the prototype. To find the right balance between included and excluded locations requires one of two things, either a lot of analysis or a remarkable amount of insight into what you like and what will be the most satisfying combination of essential parts. It really helps to be conscious of exactly what aspects of the prototype you are trying to replicate, without actually knowing ahead of time what will fit in your space.

In general, since your space is fixed, the more essential parts you include, the more you need to compress each of those ‘must have’ items. The big question is: is it better to leave out some essentials and model the remaining ones at a low compression (faithfully), or, is it better to include all of your essential parts at a much higher compression (more squished) and make compromises in the spaces in between?

More to come on this topic.