Roster

Many things enter into the car fleet.

What railroad are you modeling?

What railroads does it directly connect with?

Where does your railroad's customers get stuff from?

Mix depends on your traffic mix and era.  Traditional mix is 50% home road, 25% direct connections, 25% other.  Modern mix might be 50% private owner, 25% home, 25% other.

When I worked in Texas, the majority of the cars were private owner because of all the chemical companies.  Gons were either home road or eastern carriers (drill pipe and steel products).  Grain was mostly in home road or private, consumber goods and auto parts were in connecting and other carrier cars.

Car type mix enters into it.  There are two types of traffic, the cars that serve the customers on your layout and the cars that serve customers beyond your layout that pass through your area.  If you were modeling someplace in central Texas along a N-S route about 25% of all the cars you would see were grain cars going between the plains and the Gulf Coast. If you were modeling central Nebraska you would see tons of intermodal and automotive cars going through, even though there might not be a ramp within 100 miles.  On the other hand, if you were on a branch someplace you could go years without seeing an intermodal car.

Pictures and location

I am not a rivet counter, but try to have some sense to what I run.

Any era where the Pennsylvania railroad is around, you'll need some of their cars--they were everywhere.

I've looked for pics of my time and location, but sometimes, a distaqnce of a few miles will change what cars you see,  When you look at pics, note what sort of cars come from far away--coal cars of various sorts don't wnader that far usually, but here on the east coast, I see Union Pacific autoracks.  If there's a specific load you want to carry, then get a car appropriate. I have a pair of Pennsy flats waiting to be built because I want to be sending a 16" gun over the rails--that essentially means I need Pesny flats.

A plan? We don't need no stinkin' plan!

I like pictures

Being as I model a railroad that was owned by two other railroads and was also a bridge route it has an interesting car mixed based on my research. With that said I have based a lot of purchases on pictures and a bits of other information I have found. With what I have found is the formulas do not seem to work for me, the formulas would be fine if I think the railroad was larger or if I was modeling the main east west line. There were also a lot of captive cars which had specific blocks of cars assigned to specific customers.

I would love to find some actual train lists or switchlists from my era to help fill in the gaps, but as of yet I have not been able to locate any. The best would be actual trainlists or traffic reports from the company. I find research to be part of the challenge and also part of the fun.

Great Question.

Pictures

This is a great question.  I find myself searching out road names in pictures based on a period search of my modelled road.

Period search meaning...PC 1968....PRR 1950....Conrail 1978.

I would suggest looking at/searching your Road's Historical society's website if it has one. 

Or try http://www.railpictures.net/

I guess I’m lucky.

I just walked around the yard and took pictures.  I looked at books, drove and flew around and looked at the specific industries,

I model local and now, even though it ends up to be last year.  I knew the industries before I started to buy this batch of railcars.  I have to admit that I’ve got railcars for sale that come from an older era and are not used anymore.

Shows and swap meets are a good place to start to buy older production models.  This is followed by online offers.

Nick

Videos can be frustrating...

This subject reminds me of one of my biggest pet peeves when it comes to railroad videos. I can't tell you how many I've watched, hoping to get info on the cars in a certain train, only to have the guy making the video zoom in on the locomotive and then snap quickly to follow the locomotive as it passes. I call it "Gulash Whiplash". I wish they all would put the camera on a tripod, and WALK AWAY. Leave the camera focused on one spot as the train passes. Let us see the consist, the entire consist. I guess a lot of railfans are only interested in locomotives. I'm more interested in the cars, but rarely get to see very many. You might see a car or two right behind the power, then maybe the same just before the caboose. Watching most videos you would think every train was the power unit or units, maybe three or four cars, then a caboose. Its really frustrating, and I think sad that all that potential information is lost when it was right there in front of the camera. 

So, I still watch videos hoping to get some car info, but photos have been more productive. Find photos of the era and area you are modeling, and take note of the specific cars. I've also been fortunate to get a switchlist from one of my major industries which is a great source of info.  I keep hoping to stumble across some wheel reports some time. Research your industries as much as possible, know what they got, and what they shipped.  

Randy

ORER

This answer is in reposnse to the original question about wanting to get a prototypically representative mix of cars.  If you don't care what your mix is and buy anything that strikes your fancy, fine, but that's not the question.

There are many ways to get the "right" answer, but using the national fleet sizes as the basis is definitiely a way to get the "wrong" answer for most model railroads.

Lets say you are modeling southern California in 1953.  In 1953 the PRR had more GL and H21 hopper cars alone (just two classes of over a dozen PRR hopper types) than the ATSF had all types of cars lettered ATSF.  But seeing a GL or H21 hopper car would be rare.  On the other hand ATSF cars would be everywhere.

I follow the 50/25/25 idea...

...that Dave1905 mentioned with respect to roadnames, sticking to western roads mostly (California theme).

As for types, following research on what kind of industries where present on my subdivision during my era (including the industries beyond my layout) i am making up a fleet.

For the number of cars, i am still reading about this, ie how many cars can the layout support but thats a different question.

Cars to tell the story

You can use cars to tell the story.  In Phillie, the Inquirer newspaper was right next to 30th St station and for years (1974-1979) every single newsprint car was a CN (or CN subsidiary).  There  was one food processer in West Phillie, near 52nd St, that recieved Buffalo Creek 40 ft boxcars of flour and "Golden Loaf" covered hoppers.  Those were the only places that I ever saw those cars.  On my layout I have a textile mill that recieves cotton bales.  I try to use southern road boxcars to deliver the cotton.  Flour mills recieve grain in boxcars from the upper midwest.

Many professional railroaders can watch a train go by, on a territory they are familiar with, and by the mix of cars on the train, pretty much tell what train it is or where its going.  By selecting  a good mix of cars, you can add to the "ambiance" of the layout.

A MRH article of interest

You might look at this for a deeper discussion of gitting an approate car fleet.

https://forum.mrhmag.com/magazine-feedback-was-ezines-891776

50-25-25

every rule has exceptions

50-25-25

I encountered the accounting records for the St Joe Belt Railroad  in St Joe, MO in 1910 (the ledger books were being used as a decoration in an office).  They had the car hire records for the railroad.  While those are not a car count, more car hire is roughly comparible to more cars.  When I looked at the roads represented in the car hire records, they roughly were close to the 50-25-25 proportions (assuming the owner roads of the St Joe Belt were "home" cars.)  I also had access to many car records on my job before I retired and the modern 50-25-25 (private, home , other) was pretty close for large parts of the UP.

Looking at actual railroad car records it seems like a pretty good ratio to me.  Granted the percentages will vary a bit, but the overall relationships are pretty decent.

Era / Class / Region

What era is your operation in (steam  / transition / diesel )

What  class I railroads were 'alive' in that era (1950's had PRR/ NYC/ UP/ BN /  IC/ B&O/ C&O/ Sou /ertc as Class I RRs, and, thus their rolling stock could appear in varying percentages ANYwhere- except, maybe on short lines near you )   Class II RRs would contribute a lesser number of cars, and so on.

Region... where is your  model... what else was nearby?   I have yet to see a Florida East Coast snow plow.. thus I make my last point.

Also, geography, industry, and transshipment will dictacte a bit  PRR: coal,  NYC, Erie: Reefers,  Chicago and great lakes region:  steel, iron ore.

 "Mr. Brock came to this

This reminds me of photos showing SRR boxcars of box shook on the Visalia electric. Why would they need to import box wood from the south east considering all the wood available on the west coast? 

As for the larger question of freight car fleet, it really depends on the layout and one's interests. If you just want to play with trains you buy what you like and run it. If you want a more realistic fleet you research lines like you are modeling and learn what they featured . Prototype lines can vary from bridge routes where almost anything shows up to branchlines where only one type of car ever runs. Note that  alot of modelers do a bit of both, we build things we like that don't fit our layouts then display them or run them when no one else is looking :> ) I'd be flexible with my purchases as I gained more insight into what I need and if you end up with stuff you don't need later you can always sell it on ebay and use the money to buy other used cars. Often the best way to learn about something is to experience it first hand......DaveB

Well I don't have an exact plan

First:  Since I follow the the Maryland & Pennsylvania RR of the early 50's, there aren't many home road cars needed.  Mostly a few MOW, boxcars, and flats.  Since the raiload interchanged with the PRR and B&O, I try to have cars from those lines.  I also favor other railroads that ran in the Mid Atlantic states. 

Second: I try to have a mix of cars that reflects the time and the line.  For example, coal was a common heating fuel - most every town had at least one coal dealer, so a fair number of hoppers.

Third:  I include cars that just appeal to me like the Waddell hopper cars or pickle cars.  I also have a number of bill board reefers even though they don't quite fit my era.

Fourth:  I include fantasy cars like the Gorre & Daphetid.

Fifth:  I buy cars that are bargained priced even if that means too many UP cars.

So while I am not as rigorous as others, I do try to not have anything later than 1954. 

Paul

Oddballs

There will always be the occasional oddball; a friend of mine told me that she saw some Boston and Maine boxcars in California at one point, long ago.  If there's a particular road you're fond of, but it's far from your localle, yuo can usually justify a simple boxcar from that line, or prhaps a gon or flatcar that was carrying something coast to coast.

"a friend of mine told me

  Yeah, I remember seeing a bright blue boxcar with the big B&M logo in Fresno on the SP around 1958 or so. It stood out due to it's color. I also recall a CofG boxcar with the big cigar band logo in the Santa Cruz yard sometime in the 60's. .....DaveB 

Odd cars

We see some RBM&N hoppers of anthracite coal come thru Omaha on their way to Idaho every so often.

odd cars

re: Videos can be frustrating...

Building a freight car fleet

Before you begin purchasing a bunch of freight cars you should answer some questions and determine the following for yourself:

1. What time period am I interested in (think decade)
2. What railroad am I interested in.
3. What area of the country am I interested in.

Answer those questions and you will be a long way down the road to determining your freight car fleet, and save your self a lot of money. Also I recommend that you check out the following threads started by Jim Six, One Town Layouts  [topic:id=32127], and Modeling 1900-1940  [topic:id=31700]  Both of these threads have good information regarding choosing a location and a freight car fleet. While they may not directly address what you want to model they provide good insights and principles.

As an example I protolance an Erie branchline in Bluffton IN in the 1950's. The PRR and NYC are big players in the area. I The PRR had the largest fleet of cars followed by the NYC. The PRR had around 20,00 X-29 boxcars. this one class of boxcars was larger than many railroads entire fleet. So in my case what I model should be about 25% home fleet and the balance foreign roads. Since I interchange with the NKP on the layout, that road will have a little heavier weighting of cars than would be normal.

The key is to develop a fleet that seems reasonable for what you are modeling.