CSX basically uses the ex-P&LE main line (Youngstown-Pittsburgh-Connellsville) on the western banks of the Ohio, Monongahela and Youghiogheny rivers. CSX occasionally still uses the ex-B&O secondary "P&W" mainline along the eastern bank of said rivers, forming a sort of corridor to separate direction of traffic flow.
NS uses the ex-PRR "Fort Wayne" line on the eastern bank of the Ohio river which includes Conway Yard. NS uses both the ex-PRR "Conemaugh" and the ex-PRR trackage through downtown Pittsburgh to reach Harrisburg and points east. NS also uses the "Mon" line which is located higher up the hill along the western bank of the Ohio and Monongahela rivers. The eastern and western lines are connected by means of the Ohio Connecting RR Ohio river bridge just north of Pittsburgh. Check out my earlier thread here:
viewtopic.php?f=8&t=5348Here you will find system maps and traffic charts:
http://railsandtrails.com/Maps/P&LE-1960/index.htm, which gives you a good overview of the situation before Conrail;
http://www.multimodalways.org/docs/rail ... 7-1985.pdf, shows Conrail's trackage and trunk lines around Pittsburgh;
http://www.multimodalways.org/docs/rail ... %20Map.pdf, schematic map of CSX' Baltimore-Chicago corridor through Pittsburgh;
http://www.multimodalways.org/docs/rail ... 1-2006.pdf, NS system map with Pittsburgh inset.