The size of rail reflects the type of railway a model is. Big heavy rail denotes a mainline with heavy traffic, light rail a little used branch line. Rail weight affects the maximum axle load the track can take. If the rail on a branch is too light, some locos might not be able to use that branch.
The O-scaler is lucky in that it is fairly easy to match prototype rail height to a rough scale equivalent. No such luck for the N-scaler, for whom even the finest model track scales out at heavy-duty main line.
Model rail size is described as "Code", with the number being the height of the track as the decimal fraction of an inch multiplied by 1000. Thus code 100 track is 0.1" high.
Prototype rail is described by it's weight in pounds per yard of rail (lb/yd), or at least it was before metrication. I'm sure there is a metric standard, but as I'm stuck in the 1920's I don't care!
The following chart gives us prototype rail and the scale equivalent for O-scale (1:48) in model rail code. I've stolen this information from the Da-trains website: http://www.urbaneagle.com/data/RRrailsizes.html, and it is to American standards. That's close enough for my purposes, though.
Rail lb/yd
75
70
65
60
55
50
45
40
35
30
25
Code
100
96
92
89
85
81
77
73
69
65
57
Model rail track is available in Codes 100, 83, 70, and 55.
On the Victorian Railways 30" narrow gauge ("Puffing Billy") lines here in
Australia, rail weight was 60lb, with some
66lb on curves. Maximum loco axleload was 9.3 tons. The 60lb rail was second hand rail from broad gauge branch lines.
The Maine two-footers were originally built with 25lb rail, but most quickly upgraded to 35lb rail. 56lb and 60lb rail was later introduced onto some sections of the WW&F and the SR&RL. Only the Kennebuc RR persisted with 25lb rail.
Early tracks on the 3' gauge Denver & Rio Grande were laid in 30lb rail increasing to 45lb and finally to 70, 80 and 85lb at the end of operations, by which time it had also gained a "Western".
Little brother Rio Grande Southern ran on 50lb rail, as did Californian roads North Pacific Coast and South Pacific Coast. The Southern Pacific Narrow Gauge lasted a bit longer than others, and ended up with 55lb and 60lb rails.
Rail weight on the F.C. Antofagasta & Bolivia, a 560 mile trans-Andes 30" line that ran
from northern Chile to Bolivia, was
originally 36lb, being increased to 50lb and finally to 65lb. Locos were
mostly "large" 8-coupled locos of American, British and German manufacture.
Diagrams for many of the larger locos noted them as needing 60lb rail. The maximum axle load for locos was 12 tons, but more normally 10 tons.
The North-east Dundas Tramway, a 24" line in Tasmania, used 42lb rail with an axle load of about 9 tons. Once again second hand rail was used.
The Estrada de Ferro Oeste de Minas, a 465 mile 30" gauge system in Brazil, was built using 35lb rail.
The Barsi Light Railway, a 200 mile 30" line in India, was built with 30lb rail, and had a maximum axle load of 5 tons. Later Indian authorities authorised a 6 ton maximum axle load on 30lb rail.
The length of sleepers often comes up in discussion groups, and some claim "it doesn't matter, do whatever length looks good". That is fair enough as far as it goes, but for the prototype it did matter. I've looked at alot of dimentions for track of a number of gauges, from 2' to 5'3". The sleepers all appear to be 2'6" to 3' longer than the track gauge, whatever that is. I'm no railway engineer, but I guessed that the sleepers stick out so they can "catch" the ballast, and stop the track twist out of gauge. As always, a reader of this web site was able to give the correct answer.
Tim Harkey, a freight conductor and locomotive engineer on the former Santa Fe, offered the following exlanation: "In basic terms, the ties do hold the ballast, but the length of the ties is a function of the weight carrying capacity of the track. The longer ties provide a wider foot print and a more stable roadbed. With the gauge of the track being 3 feet and the typical width of the freight car being 8 feet, a 6 foot tie would keep the track from twisting. Just as an example, on the standard gauge track, the ties have extended to a 9 foot length as the weight of the equipment has increased. We are having precast concrete ties installed on our mainline, and the wood ties that make the transition from standard wood ties to the concrete ties are 10 foot long ties."
There is little prototype information available, but the Victorian Railways "Puffing Billy" lines used 5'6"x8"x4" sleepers, while the F.C. Antofagasta & Bolivia used 6'x8"x5" sleepers. A number of American roads had ties about 6' long, including the D&RGW, RGS, NPC, SPC, SPNG, and NCNG. The C&S was something of an exception with 7' ties. Logging roads had ties in a wide variety of lengths, ranging from 4'11" to 8', but once again tending towards 6' overall.
Some claim that narrow gauge sleepers should be especially long, and for that reason don't like the Peco track. Certainly no railway would use sleepers longer than they need to. Lumber costs money, even a few inches more over thousands of sleepers quickly adds up. Longer sleepers are more difficult to transport, heavier to carry, and harder to lay. So unless a narrow gauge railway had access to a bulk job in second hand standard gauge sleepers, I can't see why they would use longer sleepers for no good reason.
For those interested in American 3' gauge railroad tie and rail size, there is an excellent article in the Nov-Dec 1989 Narrow Gauge and Shortline Gazette, by Russ Simpson, entitled "Narrow Gauge Rails and Ties". Much of the information on American lines in this article came from that source.
Many modellers lay their own track - not for me, thank you. There are two choices when it comes to On30 track. Peco (UK) make lengths of flex track, and left, right and Y turnouts (switches), all in code 100 rail. Micro Engineering (USA) makes flex track in codes 100, 83, and 70 rail, but no turnouts. The Micro Engineering track has longer, but narrower sleepers. The Peco sleepers scale out at a little over 5'x8"x6", while the ME ties are 6' long.
The C&BFT was originally laid with fairly light rail typical of narrow gauge railways. The early locos I envisaged running would have had an axle loading of under 7 tons. Thus 35lb rail would most likely have been acceptable. With the construction of the Walkerville Railway the C&BFT main line was re-laid to VR standards with 60lb rail.
Peco track is quite similar to the VR track, as the sleepers are about the same size. Code 100 track is too heavy for 60lb rail, but code 85 is too light. In the context of an O scale model, the extra size of the track will not look too out of place. There are a set of turnouts available, and, if I want any special trackwork, for instance curved turnouts, or double slips, Peco manufacture a full range in HO gauge which could be converted. Further Peco is a reliable range, and available at my local hobby shop. So Peco is a logical choice for the main line.
I hope to model the Mt Misery branch, which was never converted and still has 35lb track. Code 70 rail is almost an exact match. No turnouts are available, however there are turnout kits in code 70 that can be used. Fortunately there will not be too many turnouts on the branch, so that may be an adequate solution.