Frederick, MD to Waynesboro, PA on something other than 40/144?
I'm not from the area (nearing the end of a meandering coast-to-coast loaded tour). I'm in Frederick now and will head to Waynesboro tomorrow-ish to visit an old friend.
I rode 40/144 (the signed route) from Cumberland to Frederick and I'd rather not backtrack on 40 to go to Waynesboro. Is the road through Yellow Springs OK to ride on? I imagine it's steep, but that's alright (I guess... ).
Yellow Springs is fine, Hamburg is really steep (gets you up on the ridge) and see a bit of traffic but people bike it all the time so they are used to seeing riders. Your other option would be Shookstown to Gambrill Park Rd, but it's still plenty of climbing. Rt 17 sees a little traffic but is not bad and mostly scenic. Overall your route is much better than 40/144. If you want less traffic pick up some of the smaller roads, but there are quite a few dirt roads out that way, so if you aren't into that you'll want to avoid them but I didn't notice any on the route you laid out. If you want to find where they are you can check dirtdata.org