Two suggestions first comes

Two suggestions first comes in my mind aside others:

http://modelingthesp.blogspot.com/2013/02/keeping-model-car-fleet-under-control.html

Tony Thompson Blog in several post (browse it have set some basic concepts for a freight cars fleet.

and " modeling the CNW in Milwaukee, 1957" ....

This guy do a very detailed blog on freight traffic, historic waybills, ORER etc... I found it's very informative.

http://cnwmodeling.blogspot.com/?view=classic

Have a nice trip on this too.

Sincerely

General Ratios

Home-foreign rations vary by era and by the traffic base of the railroad.

The older the era the more home road cars.  An 1860's layout would be upwards of 75% home road.

The newer the era the more private owner cars.  A 2010 layout should have about 50% or more of its cars end in the letter "X".

For the 1950's I've heard rations of 50% home, 25% interchange and 25% other.

Having said that, the traffic base has to be taken into account.  If you model a coal mining region prior to the 1980's or 1990's, then your percentage of home road hoppers goes way up (actually pretty safe bet for any open top cars).  If you model a gateway interchange then your percentage of home road cars goes down.  If you have a perishable train and are modeling in the east, then the number of "other" cars goes up.  The more tank cars you industries use the more "other" cars you have.  Chemical covered hoppers (which would be very few in the 1950's) drive other up, but almost all the other bulk commodities drive home road up.

Really rough way to figure it out.  Find some pictures of yards in your area and era.  If you are freelancing pick the road most typical of yours.  Count the number of cars that you can identify the type.  Then count the number of tank cars.  They will be "other" since 99% of tank cars are private owners.  Then for the tracks you can identify the owner of cars by paint scheme or reporting marks (or car type, e.g. B&O wagon top box).  Count up the home and foreign cars (except tank cars).

Find a picture with 240 cars in it.  15 are tank cars.  You can identify the owner of 92 cars  40 are home road 31 are interchange and 11 are other.  15/240 or 6% are tanks.  Of the remaining 94%, 40/92 x .94 or 41% are home, 31/92 x.94 or 32% are interchange and the remaining 27% are other.  Obviously, there are all sorts of chances for error with a small, non-random sample like this, but it can give a starting point. 

You have to develop the car fleet that supports your layout, regardless of what the prototype does.  For example the second most common car type produced for my era is the reefer.  The second most common availability of decals is for reefers.  Guess what type of car is one of the least common on my layout.  You're right, reefers.  Only a few percent of the tonnage my railroad hauled was ag/food products and that has to be split between grain, livestock and food.  So regardless of what the prototype had, I have way more reefers than my railroad really operated.  (The corollary to that is that coal and stone products are two of the largest commodities and guess what one of the least produced cars for my era is?  You're right hopper type cars).

My take on the subject

Foreign road cars, unless they were in captive service of some sort, were commonly stenciled "WHEN EMPTY RETURN TO HOME ROAD (or some specific location) VIA REVERSE ROUTE"  If the local freight agent happened to have a load going that way, they might use the empty car, but they might also have used a home road car if possible, to get a little extra money for the railroad.

That means that foreign cars of any sort should either be coming in with loads or running through, but generally not being spotted for loading.  Regional cars would be more common than others, unless some load comes from only one part of the country or is handled by only one railroad.  Special circumstances (like a cooperative agreement between to railroads, or both being owned by a parent company) could of course influence things as well.  In general, though, I'd say 50% home road, 30% regional, and 20% other would be a good mix, and would help further identify the location of the railroad in the world.

My knowledge is based on the transition era (and current RR practice, but that's a different ball of wax), and should be roughly applicable to everything from the '20s to the '70s, maybe a little more.  As has been said, later eras would use a lot more private owner cars with no real thought to region.  Today, we still see a fair number of home road cars, though many are for specific commodities and tend to be in semi-captive service, but there does not seem to be any difference between regional and non-regional foreign road cars.  The mix seems to be about 30% home road, 20% foreign, and 50% private.

When Empty Return to

"When empty return to..." cars are in a pool.  General service cars can't be put into a pool.  A plain old boxcar would not be stenciled with a return.  An auto parts boxcar with load dividers and assigned parts racks would.  A 55 ton hopper would not be stenciled. A hopper that had been modified with a solid bottom for ore service would be stenciled.

Foreign line (or home road cars for that matter) cars would NOT be stenciled unless they were assigned to special service. 

Pool service?

I don't know, Dave.  I've seen a lot of old Southern box cars with that sort of stenciling on them.  Sometimes it specifies a location (and I can definitely see those being in pool service), other times it's just "return to home road."  I always figured that Southern didn't want to pay the per diem charges for their cars being on a foreign road any longer than absolutely necessary, especially once the car was empty and no longer generating revenue.  I know that some (all?) railroads put a fairly low priority on moving empty foreign cars back home, but somehow I doubt that little request on the side of the car made any real difference.

Maybe Southern was the only RR to do that? 

you rent the car, not the track

Actually, the road the car is on pays the per diem, not the owner of the car.  The IPD cars of the 70s made most of their money just for being off of home rails.

Silly me

Duh..  I should have known that.  Ignore me, I'm going back to trying to get some rest now.  Sorry for the confusion!

I've seen a lot of old

A lot of boxcars have interior appliances (load dividers, moveable bulkheads, racks, tie down fixtures, the infamous "shackles", etc) that may not be visible from the outside except by the stenciling of the car type (XL, RBL, etc) or a trademark for the device (LD, LD2, Evans air pack, Cushion car, etc).

There are some AAR car orders that require returning car types back to railroads empty, I believe the N&W had an order that its hoppers not be reloaded.

Regardless of whether its prototype or not, I know a lot of people do the "when empty return to...." thing on their car cards because it helps the operator know what to do with an empty car, instead of them trying to guess the geography based on the car initials.

From what my research has told me thus far..

...is prior to the late 1970s (or early 1980s) during the Carter Administration, a new law was passed deregulating the railroads.  Up until that time, all rates for what railroads charged were determined by the govt, and that the amount of money a particular railroad got for shipping a product, was determined by the distance that product traveled on its own right of way.  I'm still a bit confused how it things worked as to once the car was empty, what was the charge for not returning the car, and/or what was the requirement to return it within so many days, etc.  I have read in some posts to inquiries on THAT subject, that a car from out west could be stuck out east for quite some time.  Now since the beginning of the "per-diem era", things changed where railroads are charged by the car owners for each day an empty car is not returned to the home railroad. 

But right now I'm more concerned about how many foreign cars that would be from customers that  are quite distant from in this case western PA. Now the freight car fleet will be predominately coal traffic.  The railroad will have my own hoppers (and those of the New York Central since the P&A is a wholly owned subsidiary of the NYC) as will as having AM and NKP hoppers since I am modeling a coal branch of the AM that interchanges with the P&A in southern PA off it's Big Sandy Subdivision.  But I do also want to have a sizable general merchandise car fleet (i.e Box Cars, Flat Cars, Gondolas, Reefers, etc)

Ken L

 

"Find some pictures of yards in your area and era."

 Then find some more :> )  Nothing like going right to the source. .DaveBranum

money money money

There are two types of car hire charges:  per diem and freight charges.  Per diem is the amount the car owner charges to any foreign road that its car is on, and the freight charges are billed either to the shipper or consignee, depending on the arrangement for each shipment.  A car owner charges per diem on a daily or hourly basis, depending on era, whether the car is loaded or not.  The freight charges are billed per shipment.  There are also storage fees for keeping cars on railway owned tracks after a certain amount of time if the car is waiting to be spotted, and I think the per diem is waived for a couple days after the car is spotted to give the shipper or consignee time to load or unload, but I might need correction on those points.

The main reason a railroad wants its cars back is to protect its own customers' shipments.  The per diem is incentive for a railroad to get cars off its tracks and onto a connecting road.  An empty car is not generating any revenue for any non-owning railroad, so it's in everyone's interest to get it back onto home rails where it can be the owning railroad's problem to get it loaded again.

Demurrage

The shipper or consignee has a contracted amount of time to load or unload the cars (or containers). Failure to return the car or container to its owner in the contracted period of time is billed as demurrage, and once the shipper or cosnignee is on demurrage any events (strikes, force of nature etc.) are still billed as demurrage.

Regional Cars

Ken

This would be my approach. Look at the roads in the area that you are modeling.  Next compare the size of the fleets of the regional roads around you.  Since you are modeling western PA you are going to have a lot more PRR and B&O than most other roads. They are the 800# gorillas in the area along with NYC.

Other regional roads that would show up are Erie, DL&W, LV, NKP. I would then pick roads roads that service the Buffalo, Pittsburgh, Akron, and Cleveland area. 

Beyond that I would gradually branch out to other larger roads and pick a few of their signature cars per Tony Thompson's article.  The real answer is if you are happy with the ratios that you develop then its right.

Have Fun

Up until that time, all rates

They were regulated by the government and were published in public tariffs.  They weren't necessarily set by the government.  Generally the division of revenue was by the mileage in the tariff rate with additional amounts for  the originating and terminating carriers.  The actual distance hauled had nothing to do with what the railroad could charge.  The rate was the same between two locations regardless of route.  If the rate was $10 a ton between KC and LA, then the ATSF would charge $10 a ton to haul it in a straight line and  the UP would get $10 a ton to Haul ip up to N Platte, then to Salt Lake City and down to LA.

There was no requirement to return it in any amount of days.  Railroads paid per diem (whoever had possesion of the car at midnight paid for the previous day)  Per diem has been around for the last 100 years or more.  The change in the 1980's (I think) was they did away with per diem and went to "car hire".   Car hire is an hourly charge.   That eliminates the rush to interchange cars right before midnight.  The goal is to return them ASAP.  Current car hire rates run in the 50 to 90 cents an hour range.  In addition private cars may have a mileage charge (which really doesn't affect when they are returned). 

There is no requirement to return cars in any time frame. 

The per diem/car hire applies loaded or empty.

Per diem really has no bearing on the car mix.  It only affect how you handle the foreign cars/trains going to interchange.  Since you are paying per diem on any loaded cars too, its not just the empties.

You cannot control whether you get foreign cars, since that is controlled by the origin road.  If the UP loads a PFE reefer with oranges and ships it to Pittsburgh, there really isn't anything you can do about it.  If the PRR loads a CNW boxcar with nails and ships it to a destination on your railroad, there isn't anything you can do about it.

Oh by the way, you will pay the NYC per diem on their cars too.  Subsidiary or not, if you are a separate railroad, you pay just like anybody else. 

My goal is that every 12 car train will have at least 2 P&R cars, one PRR car and one B&O car.  I have about 120 cars on the layout and I currently have about 25 P&R open top cars and shortly will have 10 P&R boxcars (all my home road cars have to be kitbashed/scratchbuilt/craftsman kit built).  Eventually I would like to have about 10-15 P&R coal cars in each direction over my layout per session.

Pictures of yards

Pictures give the best evidence, but not perfect evidence.  Pictures are taken from spots where the vantage point is good.  So it may be the south end of the yard is the one photographed most often because there is a bridge there that gives a "good" look at the yard or the engines on outbound trains, etc.  Because yards have certain destinations in certain tracks, and which cars in which tracks tends to be more static (yardmasters are creatures of habit too), it may be that those destinations may skew the photographic evidence. 

Lets say track 12 is nearest the camera and it happens to be a track with cars for Chicago.  So out of 24 cars visible 12 are foreign line cars.  So the yard is 50% foreign?  Not necessarily, it could very well be  that every other track in the yard is filled with home road cars except that the track with cars to an from Chicago have foreign cars. Out of 180 cars in the yard 24 are foreign, or 13%, but the photo leads you to believe its much higher.  the suggestion to look at multiple pictures is well taken.

Mixing charges

Car hire replaced per diem.  Its either or.  1950's its per diem.  1990's its car hire.  Now people will call car hire per diem just because they are used to the term (just like they call an air brake valve a "triple valve", which were banned from interchange service back in the 1930's or so).

Freight charges are the charges for performing the transportation service.  They aren't car hire.  they really have little or nothing to do with the car itself.

The "storage" fees are called demurrage and they are paid to the railroad that has possession of the car.  They are a daily charge.

Per diem/car hire is paid by the railroad that has possession of the car to the car's owner.  There is no waiver of per diem or car hire.

All very true.  The exception is when the railroad doesn't have enough cars to protect its loadings and so keeps foreign cars to protect home loadings.  Back in the 1980's some of the eastern roads were short of gondolas.  Often western roads were reluctant to use their cars to send shipments to some eastern roads because the eastern roads would keep the gons to protect their own loadings.  the eastern roads didn't have the money or didn't have the time to have their own cars built, so it was cheaper to pay the per diem /car hire than to build more of their own cars.  Granger roads would hoard 40 ft boxcars around harvest season because it was cheaper to use another road's cars for a month or two than it was to build a bunch of their own cars for only one or two trips a year.

One has to remember that back in the pre-Staggers days, if a boxcar got a loading twice a month it was outstanding.  Even today an extremely well utilized car only gets a load once a week and some specialty cars only get a load once a month.  A plastics covered hopper might get 2-3 loads a year.

"Pictures give the best evidence, but not perfect evidence"

Ideally the best option would be to find someone who has actually seen the place and era you want to model. Specific spots on a railroad might have very different car types and numbers than the railroad as a whole.For instance to model the SP santa cruz branch in the mid to  late 50's one would need Gp-9, and SD-7/SD-9 for power. Lots of SP hoppers and GS gons for sand service, a few 2 bay cement hoppers, a  few flat and boxcar lumber cars from north state SP and pacific northwest roads, depending on the season some PFE 50 foot mechanical reefers, a seasonal fleet of mostly SP and Cotton belt boxcars for the canneries, a smaller number of year round boxcars for local manufacturers, a small number of foreign road cars for incoming products from the east, and for one summer around 1957 a work train of old SP equipment parked in the yard. Bringing up the rear would be a wooden or steel sided cupola caboose. A nice little fleet of cars pretty easy to model other than the SP hoppers which have been made but only in limited quantities in HO scale......DaveBranum