On Aug 19, 2008, at 10:55 AM, Mike Brock wrote:

Well, I don't have the data from the Southern train but I do have Tim's
results from his 1947 UP data and, of course, I have the 1949 UP
data...which I copied to Tim and he analyzed. The theory worked fairly well
with the 1947 data...777 box cars...but the 1949 data...almost twice the
size...1325 box cars...in Tim's words "blew it all to hell".

If, however, we had the data from
3 RRs to work from and the data from the largest did NOT support the theory,
I would try to alter the theory to match the data or accept the theory at
great risk. Unfortunately, this is the case when one applies the theory to
the 1949 UP data. IMO. If what I am saying is incorrect, please let me know.

Mike,

I think Tim may have overstated the divergence of the 1949 data from the theory <G>. The difference in 1949 are those annoying extra SP cars... with the exception of those, the national fleet model is still pretty accurate, correct?

If you did not have any knowledge of the 1949 wheel reports, how would you set up your fleet?

I have looked high and low for wheel reports, or for that matter even tower sheets from my chosen period of June 1944 for Columbia PA. I have found nothing. Nada. Photos are rare due to wartime concerns. Films do exist, but mostly on other parts of the PRR (they tend to confirm the Gilbert fleet model and the Brock NP model). So, what should my starting point be?

As I see it, there are two major competing models being espoused (for boxcars)

1) The loco-regional interchange model. This model says that by virtue of proximity, connecting road percentages will be higher than roads that are further away. FWIW, that does not mean that if distant road X has 10% of the national fleet and close road Y has 2% that there should be more Y cars than X cars, but only that the % of Y should be above 2% and by default, the % of X must be below 10%. No data sets have been offered to support this model.

2) The national fleet model. This model says that because boxcars were freely interchanged that the % of a given car seen on any given railroad over time should approximate the % of the car in the national fleet. Model 2 is supported by several small data sets.

Additionally, there are data sets such as the 1949 Fraley and the Potomac yard set that do not appear to match EITHER model exactly. In both these cases, one to several roads appear to be "out of kilter" compared to the rest.

Railroad historians can argue the whys forever, but I have a layout to populate, so, what does this mean to us as modelers?

For you (Mike), is 1953 like either 1949 or 1947 or is it different still? Does the fact that there's a war on make a difference? Do we just throw up our hands and say it is unknowable, there is no perfect model and I'll just put anything I damn well care to on my layout? (we'll call that model 3 <G>) I've always held that the national fleet model is a STARTING place and that arriving at a realistic fleet is an iterative process. It's not that the model is wrong and useless, it is that 1949 on this line is a case where the model needs to be adjusted. Both 1947 and 1949 follow the national fleet numbers for most of the fleet, so why not start there and then perhaps increase the SP numbers slightly, maybe 50% over expected numbers? To model this line using the loco-regional model might result in the correct % of SP cars, and the incorrect % of just about every other road. I don't view that as a logical solution ;^)

My point is that while the national fleet model may not predict with 100% accuracy, it is a STARTING place, and in the absence of any other data, provides you with a reasonable representation of the steam era (based on the data sets). If someone is lucky enough to develop additional data sources, then those can be used to modify the national fleet model to represent some of those local deviations. Situations that might be included would be some that have been named, such as grain rush season and areas dense with automobile manufacturers (and hence assigned service cars).


Regards
Bruce

Bruce F. Smith
Auburn, AL
http://www.vetmed.auburn.edu/index.pl/bruce_f._smith2

"Some days you are the bug, some days you are the windshield."
__
/ &#92;
__<+--+>________________&#92;__/___ ________________________________
|- ______/ O O &#92;_______ -| | __ __ __ __ __ __ __ __ |
| / 4999 PENNSYLVANIA 4999 &#92; | ||__||__||__||__||__||__||__||__||
|/_____________________________&#92;|_|________________________________|
| O--O &#92;0 0 0 0/ O--O | 0-0-0 0-0-0