Re: Freight Car Distribution on smaller RRs


Dave,Which road do you model?Armand Premo

----- Original Message -----
From: "devansprr" <>
To: <>
Sent: Wednesday, February 04, 2009 7:18 PM
Subject: [STMFC] Re: Freight Car Distribution on smaller RRs

--- In, "Mark Pierce" <marcoperforar@...> wrote:

While the odds of any particular small railroad's car (most likely a
box car) would be on another, far-away, small railroad's tracks is
probably too small to measure, I propose that the odds of any one of
all such small railroads' cars showing up is much higher. For us
model railroaders, I say have a small fleet of "oddball" rolling
stock but rotate them on/off the layout.

Mark Pierce

--- In, Bruce Smith <smithbf@> wrote:

Folks can argue whether the Nelson-Gilbert model is valid or
not 'til
they are blue in the face, but one advantage we, as WWII era
have, is that the Nelson-Gilbert model is the RULE... since the
service rules were suspended. What that does for you in this
situation is unclear, since the M&W proportion of the national
is pretty small...say for the purposes of discussion, 0.1% In
case one M&W car would visit the YV for every 1000 foreign boxcars
that visit. Not impossible, but definitely unlikely. Normally, I
think most of us say "don't model the oddballs", but in this case,
this is a "teachable moment". The presence of occasional rare-
boxcars represents the REALITY of the WWII traffic pattern, and is
part of what is "normal" for that period of time. I have reserved
small percentage of my fleet for "interesting" rare foreign cars
precisely that reason.
Actually, there are many reporting remarks well under 0.1%. In fact an
analysis of the 1943 ORER type X and XM shows that the 100 smallest
box car fleets (per reporting mark) had a total of approximately 1860
X and XM cars - which was 0.2% of the national fleet - which would
equate to only one of those reporting marks in a 500 box car fleet.

In 1943:

The top 11 roads had 50% of the fleet. Sorry Mike, but NP placed 14th,
with 2.6% of the national fleet. But any WWII layout with at least 40
box cars needs one NP box.

For some idea of the "random" car, in addition to the 100 smallest
fleets, another 50 roads had less than 0.1% of the fleet - so Ann
Arbor (the biggest fleet of the 50), would be one out of every 1000
box car appearances on a layout.

Rather than think in terms of someone's fleet, another way to look at
it would be the number of cars routed out of staging each session.

So for a layout that moves 200 X and XM cars out of staging per op
session the Ann Arbor car would appear once every 5 sessions.

With the largest fleet, 22 PRR X and XM's would need to be moved on
scene each session. Five NP boxcars out of staging would be
appropriate per session.

But for the 100 smallest fleets, only one car, picked from a
collection of these railroad's box cars, would appear every 4th
session. None of the cars from this "smallest" road pool would appear
3 out of 4 sessions.

Another way to look at this is that 39 road's box cars would "earn" an
appearance every session, totaling 178 of the 200 boxcars appearing
per session. (Katy is the last "regular" on the list)

It would then be appropriate for the final 22 cars used during the
session to be drawn from a fleet of "occasional" cars that would not
be used every session.

18 more roads would earn an appearance at least every other session
(including well known roads such as T&P, Cotton Belt, D&H, WM & WP.)
These roads would constitute about 14 cars per session.

About 40 roads could be used for 7 more of the 200 cars - some
appearing once every 3rd session (KCS), and a few only every 20th
session (e.g. NWP).

One car per session could be drawn from a pool of 117 reporting marks.

For a volume of 200 cars on-scene per session, and assuming that after
5 sessions all of the operators have forgotten when they last saw the
rare, small road X/XM, then I would need a fleet of 178 cars to appear
every session (from 39 roads), another 33 or more cars to appear one
to four times per 5 sessions (from 33 roads), and anywhere from 25 to
147 cars with 147 different reporting marks that would appear only
once per five sessions (it would be appropriate for 5 different cars
from this pool to appear each session). Note that popular roads such
as Rutland, Clinchfield, Georgia, SP&S, DM&IR, TH&B fall into this
"once per five session" pool!

Minimum fleet would be 236 cars - upon entering staging, 89% of the
cars entering staging would go right back out, but the other 11% would
need to be "fiddled" between sessions.

This analysis is obviously very hypothetical, but it leads to a few
conclusions for a layout that moves 200 boxcars out of staging each

1) Small road cars can appear in medium size fleets, but about 11% of
the fleet may need to be fiddled between sessions (into or out of

2) For an out-of-staging traffic level of 200 cars per op session, an
additional 18% of the fleet would be required to model the "rare"
cars, assuming that everyone forgets what they saw more than 5 op
sessions ago (this pool gets larger as everyone's memory gets longer).

3) Half the cars that appear each session would come from just 11
roads. While this might seem boring, it might actually enhance the
railfanning aspect of trying to spot the rare cars - diamonds in the
rough so to speak.

Personnal lessons learned:

A)This helps justify having a significant collection of rare cars, as
long as there is a large fleet of "core cars" that can be quickly
accumulated and put in operating order (e.g. shake the box).

b) Fiddling may be a lot more necessary than originally thought, if
"appearances" are to match the "Nelson-Gilbert" model. This has a
significant impact on staging design, and tends against the "put
staging under the layout" concept. At these traffic levels, for each
train entering staging, 1 in 10 X/XM's will need to be changed out.

c) To implement the Nelson-Gilbert distribution model, a lot more car
storage will be required at the fiddle location - enough space for at
least 40-50 boxcars.

One other quick Calculation (still based on operator memories only
lasting five sessions):

For a smaller layout with 50 X/XM's entering from staging per session,

- 17 roads appear every session = 34 cars (includes one NP boxcar for

- 27 roads (and at least 27 cars) that appear at least once every 5
sessions. 12 cars each session from this pool.

- A pool of at least 20 cars, where each car will appear not more than
once every 5 sessions, with 4 cars from this pool appearing each
session. Note that this pool includes roads such as CGW, Cotton Belt,
D&H, MEC, B&M, WM, WP, KCS, CofG - so these are not "rare" roads.

- For the smaller fleet, 1 out of 3 of the boxcars will need to be
"fiddled" into and out of storage every session. Fiddle storage is
still in the 40-50 car range.

At the other extreme (not sure if anyone operates this big), for 1000
X/Xm's entering from staging each session:

- 70 roads' boxcars are present every session = 976 cars that appear
every session and do not need to be fiddled. 500 of these cars will
come from only 11 roads! (kind of boring, and kind of prototypical...)

- 31 roads (and at least 31 cars) that appear at least once every 5
sessions. 17 cars from this pool appear each session. This pool still
includes roads such as Ann Arbor, Rutland, Clinchfield, DM&IR, SP&S.

- A pool of at least 35 cars, from 119 reporting marks, with 7 cars
appearing from this pool every op session. Each car should only appear
once per five sessions. Notable infrequent roads in this pool for such
a huge layout include: Ma&Pa, LS&I, FEC (does not include ventilated
boxcars), and Virginian.

- For the huge fleet, only 2.4% of the fleet will need to be fiddled
each session. This is likely less than one boxcar per train to fiddle.
Interesting that this is almost exactly the same number of boxcars
fiddled for the 200 boxcar session. Only need around 60-70 cars of
storage at the fiddle yard (minimum).

It is intersting that while the small layout session requires a lot of
fiddling, one can justify in-frequent appearances of a much larger
percentage of the cars - it just happens that most of these
"infrequent" cars should be for pretty large railroads, unless your
operator's memories are short;-)

At the other extreme, for large layouts the major roads rule -
prototypical but not very interesting. This would add a "look out for
the odd car" concept to the op session much like railfanning the
prototype that might be enjoyed a little - "Hey, did you spot that
SP&S boxcar last session?"

Enough rambling..

Dave Evans

PS - I promise not to do this again - but I needed a long break from
some very tedious work. Sorry...


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