(I’m assuming you’re talking the Somerset area; my apologies if that’s not the case.)
I went down to Donegal a few weeks back, based on an Oscar Swan route.
In McKeesport, pick up Lincoln Way through White Oak to Clay Pike, then down through Herminie and Madison to Rt 31 all the way to Donegal.
Traffic wasn’t bad once I got through White Oak, but there’s a long climb near the end of 31; nominally 3 miles long and utterly lacking in shade, so was pretty brutal under hot sun. Good wide shoulder, though, so grinding my way along was merely unpleasant, rather than dangerously close to fast-moving traffic.
I haven’t done it eastbound, but I bet picking up 130 somewhere east of Greensburg would be a nice ride; lots more shade, and fairly pretty.