Re: Freight car Distribution

Viv Brice

Thanks, Dave,
You've taken this the next step and applied the thread to the model railroad
world. It has set me thinking on how to include the necessary car swapping
into my own layout. And I'll definitely be visiting my hobby shop.

Chuck and Viv,

The statistical "variability" of "traffic" you are hinting at was discussed
on this group back in February 2009.

I crafted a post based on a simple statistical analysis, not to prove or
disprove the basis for a specific road appearing at a specific time and
location, but simply to illustrate the probability of certain reporting
marks appearing in a sample set. (devansprr Wed Feb 4, 2009 4:18 pm ((PST)))

My focus is WWII, and I had been reviewing the Delano color photos to get a
sense of freight car weathering. A picture from Belan, NM caught my eye
since it had just four box cars in it - all eastern roads. One B&O (no
surprise - big fleet), one Wabash (not that surprising), one Erie (getting a
little rarer), and one C&WC 40' Steel Automobile car (C&WC's TOTAL X and XM
fleet was 532 cars - this is kind of like the mason jar car that caused so
much discussion on this group a year or two ago). The national X/XM fleet
was over 800,00 cars in 1943, so we are talking one out of every 1,600 cars.
Now that C&WC reporting mark, in New Mexico, was a LONG shot.

This triggered two thoughts - most railfans probably recall the odd, rare
car much more clearly than recalling the predominance of plain jane cars
from the majors of the day (during WWII, eleven roads owned half the
nation's box car fleet. Watch trains for a few hours at a busy spot, and
people of the era might forget the fact that 9% or so of the cars were PRR -
see them everyday). But a C&WC car? Where is that railroad? I have never
seen that before. Not to be forgotten quickly (and more likely photographed
too - which opens another can of worms.)

Thought two - for general merchandise box cars, not in captive service, on
mainlines that are primarily bridge traffic, some simple statistics are
probably a valid analysis tool to suggest trends. For example, if my planned
mainline model railroad has a number of freight trains that come out of
staging every operating session, with a total of 200 box cars arriving on
layout, then I doubt my C&WC model should make an appearance every op
session (I might be able to justify having the C&WC car pass through once
each session if I had 1600 box cars arrive on layout every session - not
likely ;-) If it did appear every session among just 200 box cars, and my
model railfan was counting cars (or we are counting his old home movies ;-),
then one would think that C&WC was a major road, since it would appear more
often than a boxcar from T&P, Cotton Belt, D&H, WM and WP since each of
those well known roads had less than 0.5% of the national box car fleet
(less than 1 in 200 boxcars nationally for each of these roads).

In the end analysis, statistics suggests that modelers are quite justified
in including a considerable "fiddle" fleet in their staging area so that
some sense of randomness can be added to the trains that appear on their
layouts out of staging. In fact, the huge number of small roads during the
WWII era might actually make a fiddle yard in staging a mandatory feature if
one wants to model the variability of freight car reporting marks that
should appear on a layout.

For example, if your fleet of cars generates 200 boxcar moves (traffic) onto
a layout every session, and you want to provide a prototypical sense of
randomness over 5 operating sessions before an unusually rare car makes a
second appearance, then you would draw those 200 box cars from a fleet of at
least 236 cars. At least 25 of those cars would each be from a different,
small fleet RR, and appear only once out of the five sessions. This is
because roads such as Rutland, Clinchfield, Georgia, SP&S, DM&IR, TH&B each
had X/XM fleets LESS than 0.1% of the national fleet. Each session, only
five of those "rare" 25 cars would appear on the layout. So over five
sessions, that Rutland box car should only arrive on the layout ONCE.

To further increase the sense of "randomness", out of the 200 box cars
arriving "on-scene" each session, 178 would be regulars on the layout,
representing the 39 roads that during WWII each had at least 0.5% of the
national X/XM fleet (at least 1 in 200 cars - Katy was the smallest fleet
that just makes this cut). So those 178 cars would appear every session.
From the rare "fiddle" fleet described above, five other boxcars from the
smallest 147 RR X/XM fleets would also appear each session.

But that leaves 17 other boxcars to deploy each session (200-178-5), and to
maintain the sense of randomness, those 17 cars would need to come from a
fleet of at least 33 cars, one each representing the 33 roads that did not
make the "big fleet" cut of 0.5% (39 roads), but that were bigger than the
147 roads/owners that are in the rare "fiddle" fleet. Each session, 17 cars
from this intermediate fiddle fleet of 33 roads would be selected. Note that
railroads in this fleet include T&P, Cotton Belt, D&H, WM, KCS & WP. Out of
the five operating sessions, some cars in this intermediate fleet may appear
three or four times, others just once or twice.

So now our model railfan captures on his model movie camera five rare X/XM's
out of 200 that passed his favorite train watching spot that day. But how
many will notice that, averaged over time, and assuming N-G is in effect at
this location, 100 of the 200 X/XM's that are captured by his camera on that
day will be from the 11 roads that owned 50% of the nation's WWII box car
fleet? (Boring...)

Note that all of this is just to "normalize" the reporting marks. Additional
"fiddle" cars would be required for "unusual" and rare cars that were a
clear spotting feature. For example, the GN plywood war emergency box cars
were unusual and standouts to some extent, and while GN would have several
cars appear every session, statistically speaking the GN car was almost as
rare as the C&WC car. So it might warrant a place in the "fiddle" fleet
instead of the every-session 178 car fleet. One could obviously extend this
concept to an absurd extent, and that is clearly not necessary.

But I think it might be a worthy objective, on a model railroad, that the
rare prototype cars remain rare, and that a WWII train full of one-offs
would never occur, and that instead a train with a significant percentage of
1937 ARA standard box cars (about 1 in 7 of the nation's X/XM fleet in WWII)
should be present, as should one or two PPR X29's (that class alone was
nearly 3% of the national fleet).

To highlight this point, during WWII, fully 40% of the nation's steel, 40
foot, non-PRR box car fleet was the 1937 ARA design! Fortunately for me
Branchline, Red Caboose, and Intermountain have a wide selection for that
fleet - many with WWII paint schemes.

Sooo, feel free to visit the hobby shop, and as long as you (1) restrict
your purchases to cars accurate for the era you model, and (2) you model a
location with significant through/bridge traffic (or else all of this ENTIRE
thread goes out the window, as Elden has clearly demonstrated during
previous discussions), and (3) include a fleet of about 40 or so fiddle cars
in your staging yard so "rare" cars are "rare" on your layout, and (4) your
visiting "consist" police have a memory that only lasts about five op
sessions, THEN, no one can question the stray appearance of that C&WC box
car, or that yellow one with the Mason Jar on it - once every five sessions.

Dave Evans

PS - looking at my Feb 2009 post on recommended fiddle fleets, it was a
little confusing - if I have time this weekend I may clean it up and re-post
so it is more understandable.

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