The railway lines to Auschwitz were presumably to ship in raw materials and ship out finished product.
Then what were they shipping to Belzec, for instance? Certainly not "raw materials," according to an Order Police officer of Reserve Police Battalion 133 in Police Regiment 24.
"To: Commander of the Order Police in the district of Galicia, Lemberg
Subject: Jewish resettlement
... The Jews had been informed by the above-mentioned agencies and the Labor Office to gather at the collection point. ... Some 5,300 Jews were actually assembled there at the appointed time. With all the manpower of my company, I sealed the Jewish quarter and searched thoroughly, whereby some additional 600 Jews were hunted down. ... Each car of the transport was loaded with 100 Jews. The great heat prevailing that day made the entire action very difficult and greatly impeded the transport. After the regular nailing up and sealing of all cars, the transport got underway to Belzec at 9 p.m., with a guard of one officer and nine men. With the coming of deep darkness in the night, many Jews escaped by squeezing through the air holes after removing the barbed wire. While the guard was able to shoot many of them immediately, most of the escaping Jews were eliminated that night or the next day. ... The transport was delivered to Belzec without incident.
(talking of further "actions" in his command area) On Sept. 8, some 300 Jews--old and weak, ill, frail and no longer transportable--were executed. According to the order of Sept. 4, of which I was informed of on Sept. 6, concerning use of ammunition, 90 percent of all those executed were shot with carbines and rifles. Only in exceptional cases were pistols used.
(talking of another transport to Belzec with 8,205 Jews) The slow journey was time and again used by the strongest Jews to press themselves thorugh the holes they had forced open and to seek their safety in flight, because in jumping from the slow-moving train they were scarcely injured. ... Shortly beyond Lemberg the commando had already shot off the ammunition they had with them and also used a further 200 rounds they had received from army soldiers, so that for the rest of the journey they had to resort to stones while the train was moving and fixed bayonets when the train was stopped.
The ever greater panic spreading among the Jews due to the great heat, overloading of the train cars, and stink of the dead bodies--when unloading the train cars some 2,000 Jews were found dead in the train--made the transport almost unworkable. ... Because of the special circumstances described, the number of Jews who escaped from this transport cannot be specified. Nonetheless, it can be assumed that at least two-thirds of the escaping Jews were shot or rendered harmless in some other way. ...
Westermann
Reserve Lt. of the Schutzpolizie and Company Commander"
--from documentation admitted as evidence in the Landgericht Wuppertal trial, stored now in Yad Vashem Archives, cited in 'Ordinary Men: Reserve Polcie Battalion 101 and the Final Solution in Poland' by Christopher Browning
I have more letters from Order Police officers commenting on the mechanics of transports and mass executions, but I really don't feel like transcribing them. Suffice to say, most English and German-language university libraries should have copies of Browning's seminal work, and comparable historical journals and publications.