How do the U.S railroad companies manage their freight wagons?

Question

In China, most rails are operated by the stated owned railway administration so the freight waggons are free to interchange, but as far as i konw most US rail companies are private,so how do they manage their waggons?

Answer 1

There are two ownership classes - by railroad, and by non-railroad.    

Examples of non RR car owners: TTX (formerlyTrailer Train), Union Carbide, Cargill, ADM,  GE Railcar Services, ITEL, etc.  are private companies which don't operate trains or own any trackage, but do own and lease railroad cars to railroads and shippers.

All freight cars (wagons), if they are mechanically sound for interchange, can be exchanged and used anywhere in the US.   In fact, the freight car owner can earn income for every day the car is under movement on a 'foreign' railroad.  This is called 'per diem' leasing.

Railroads use computers to manage the location of all cars on their tracks.