The US railroads do a bit of all of the above. Where I live we have Pan Am Railways, which has a number of long haul freights, drag freights I suppose, that run from one end of the system to specific yards at the other. The NOED, or POSE, runs from North Main Junction to East Deerfield, and Portland to Selkirk, NY, respectively. They then have some switcher operations at various yards, although these have been consolidated over the years, that handle the local operations. These runs are given numbers like LA-1, LA-2, SA-1, SA-2, for Lawrence Switcher 1 and 2, and Salem 1 and 2. LA-1 will run from Lawrence up north to Haverhill and above, servicing whatever local industries are on the line as well as the South Lawrence industrial park. This switcher also used to work the now abandoned M&L branch to Salem New Hampshire. In the B&M days, SA-1 and SA-2 handled the switching in Peabody, Salem, Lynn, and even some down in Melrose and Malden. At one time they used to go up to Danvers, but that operation has closed by PAR. The old B&M also had LASA, or Lawrence to Salem runs which would transfer the freights between the two yards. This was an interline freight and less of an actual local that did the switching. Today, this is gone, and the complete operation, both the switching and transfer is done by LA-2.
There are also intermodal freights on this line. At one time they ran the East Wind in conjunction with Conrail and Connecticut Southern, and another operation with the old Central Vermont. Today it's not uncommon to see stack trains running, in cooperation with Norfolk Southern and their joint operation, Pan Am Southern (PAS), running between Mechanicsville and Ayer, MA. The containers are then shipped via PAR to Portland and beyond, or are interchanged with CSX in Ayer.
Now this is only a tiny operation compared to what CSX, NS, BNSF, or UPRR runs.
As far as websites, you might want to check out railroad.net
www.railroad.net where they discuss various train operations, perhaps also do a search on Google or Bing and see what you get. There is also the opsig group at the NMRA, which is an operations interests group. In addition to direct websites such as this, I also recommend looking at satellite views of areas of interest. This too can give you a view of trains on the mainlines and branches, as well as cars on sidings at various industries.
The various industries of course vary between the regions. In the far west in northern Wyoming, you're going to see long coal trains coming out of the Powder River destined to various power plants in the country. These in many cases are run as unit trains from the mine to the power plant without any interchange, and keep the same engines for the run. Other areas will have automobile manufacturing, which will require various goods and raw materials. There is steel, plastic, cloth, engine parts, etc. all of which travel more efficiently via rail. The plastic industry requires petroleum products to produce the raw plastic pellets. The raw oil comes in to the chemical plants from refineries in tank cars, and the plastic is shipped in covered hoppers to the various plastic companies. The parts are then shipped via local truck, or even rail to other industries. Staying with our automobile industry, we're also going to need glass. For glass manufacturing, there is sand (silica), and other materials used to create the safety glass. The glass raw materials are then shipped to the glass manufacturers to create the windows, and these are then shipped to the car factories.
In forested areas, you are going to see lumber and paper, with lumber going to various industries including pulp plants to make paper, as well as to furniture and building materials industries. The paper industry also requires various chemicals, including clay, Kaolin to be exact, bleach, and acids, so your trains servicing the paper industry will have log trains, bulk hoppers, tanks, and boxcars heading up to the industries.
There are many, many other industries such as this. For a rail operation, you could have large, long manifest freights carrying raw materials, or finished goods from a portal, which represents the outside world. With our ability to control AI drivers directly in Trainz, you can take control of the through freight when he reaches a specific yard where you disconnect the engines, send them off to the engine house for service while you then have an AI switcher add and remove freight cars for the local industries. When the switcher is done, send the original AI-controlled endings back on the head of the new freight, which was made up by the switcher, and send him on his merry way. I've done this more than once and it's a great challenge getting a freight ready and prepping it to leave between a passenger train which is scheduled to pass through. Once this through freight leaves, you can send him to another portal or even another yard, you can take the switcher, or another one, and have that AI driver visit various industries and branch lines.
Anyway, I hope this helps or perhaps sparks some ideas and questions.
John