I was yarding 203 (an intermodal freight) at Inman Yard today and I noticed 4 welded rail (a/k/a ribbon rail) trains in the yard. Three of which were up on the north end in the Local Yard and the 4th was actually being loaded in real time at the rail fabrication plant next to the intermodal yard. All but one of the rail trains had a box car on the end opposite from the hydraulic loading/unloading car.
I noticed the shorted of the trains had only 18 flat cars. The longest one appeared to have about 24. This stands to reason, because welded ribbon rain is generally loaded in lengths of 1/4 mile or roughly 1320 feet. I've actually run a few of these trains in through freight service to Greenville, SC, and if I recall they're usually about 1600-1700 feet long, which stands to reason, because the time you add a few hundred feet to account for the locomotive (usually one, but I have seen two on occassion). Also the rear hydraulic car, and the boxcar(s) that are on the head end account for another 50 to 100 feet of the train length.
As someone pointed out, they indeed have only TWO racks per car for the rails to slide on. The Norfolk Southern rail trains have racks that are tall enough to hold six levels of rail. I've never counted how many rails wide each rack is. Just taking a wild guess I'd say either 10 or 12 wide. So that'd be somewhere around 60 or 72 or so rails per train. It may not be 10 wide, but I think it is atleast that wide. But say it's only 60 rails per train...that'd be 15 miles of rail (or 7.5 miles if you consider it takes two rails per mile)
Rail trains like this are often used to REPLACE worn rail. The rail is delivered on location by a crew in "work train" service. The track department will have a number of employees there to assist and direct the unloading of the new rail at the location. Then the work train leaves. At some point later, the track department will come in and replace the worn rail with new rail and move the old rail aside. Eventually another work train (empty) will be called and the track department will assist that crew in loading up the old rail to be taken somewhere. I'm not sure what they do with the old rail...I'm guessing it's melted down and recycled into new rail or other steel products.
Just in case you're wondering, work trains (whether rail trains, ballast trains, cross tie trains, etc) are the most boring of all trains on the railroad, because you wind up doing a lot of sitting and waiting. Maybe pulling ahead a few hundred feet and stopping again for long periods of time, repeat ad infinitum...trust me...very boring!
You could literally bring a barbeque grill and set it up and have a picnic waiting for the next move to be made (and I've heard tale that in the OLD days this very thing happened on some work trains where they had SD40-2's with the long "porches".
Anyway, getting back to the rail trains. Perhaps instead of trying to model a welded ribbon rail train, someone might prefer modelling a sectional rail train. It's very common to see entire trains made of flat cars (or in some cases gondolas) loaded with sections of jointed rail anywhere from 25 feet to about 40 feet long. You might have a train with 50 or 60 of these in the consist. There's no limit to how long or short, since they're loaded in individual cars rather than a "set".
Ribbon rail flats have the knuckles "locked" using a nut and bolt to lock the pin and prevent the cut lever from working. Sectional rail trains usually don't have this, as they may not all be going to the same destination. You also see a lot of sectional rail cars mixed in with various through freights.
It's also common to occassionally see a welded ribbon rail unit train on the head end or rear end of a mixed freight. Sometimes you'll see
2 or 3 empty welded rail trains moved together in a single train.