The PRR literally had something for everybody. And it was often all close by. For example, in the Altoona area you had the steady parade of trains over the mountain via Horseshoe CUrve. You had the locomotive shop, where almost everything on the system came for heavy repairs. Hollidaysburg was the freight car shop, and a hub of lightly traveled branchlines. It also had its pwn line to the top of the mountain in a mirror image of the mainline, including its own Horseshoe curve (called Muleshoe) but with only two tracks instead of four. At the top of the mountain, Cresson was a terminal which served the coal branchlines, which originated an incredible amount of tonnage, completely different from the ones out of Hollidaysburg.
One thing about PRR in the diesel era. People look at the incredible amount of different types of locomotives PRR had, and try to model one of each kind. But that's not what you would have seen if you were there. Rather than have everything roam the system, they tended to parcel out specific locomotive to certain areas where the shop people were familiar with the oddballs. The most common locomotives, like F7s and GP9s, roamed the system on the high priority trains, but things like Baldwin sharks, Alco Pas and FAs, and anything from Fairbanks Morse worked in specific areas out of specific terminals. This practice continued under Penn Central and Conrail. As these assignments shifted somewhat over the years, your best bet is to look for pjotos of the area you want to model and see what showed up on trains.
One thing about PRR in the diesel era. People look at the incredible amount of different types of locomotives PRR had, and try to model one of each kind. But that's not what you would have seen if you were there. Rather than have everything roam the system, they tended to parcel out specific locomotive to certain areas where the shop people were familiar with the oddballs. The most common locomotives, like F7s and GP9s, roamed the system on the high priority trains, but things like Baldwin sharks, Alco Pas and FAs, and anything from Fairbanks Morse worked in specific areas out of specific terminals. This practice continued under Penn Central and Conrail. As these assignments shifted somewhat over the years, your best bet is to look for pjotos of the area you want to model and see what showed up on trains.