Starting from just south of Canfield, OH, I mapped out a possible route to Pittsburgh using quiet(er) rural roads. Some of this route had been previously ridden by some long-distance cyclists based in the Pittsburgh area. I assumed the prospective rider had already arrived at Washingtonville Rd, at the south end of the Mill Creek Metroparks Bikeway. What follows is a report on the route after driving it.
Leg 1: Washingtonville Rd to the Beaver River
This was almost entirely on farm roads except for a jog through the city of Columbiana. They were generally pretty quiet, but as you might expect these roads were sometimes rough and there were a few long hills. After leaving Washingtonville Rd via Garfield Rd and Green Beaver Rd, there was a long hill and rough pavement. After that, is was mostly smooth (but lumpy) sailing into Columbiana. East of town we diverged onto Columbiana New Castle/Heck Rd. We continued to zig zag due east including Dickerson, Burkey, and Moravia Roads. There is substantial hill on Moravia. Near the Beaver River we turned south on PA-18, which has ample shoulders. We crossed the river in Wampum.
Leg 2: Through the hills and valleys SE to Cranberry Township.
Initially we were on PA-288 which had good shoulders until we entered Elwood. A couple of miles of busy "city" roads followed. PA Bicycle Route A will be encountered in this area and should be avoided. This leads to Rt 51 in Rochester and miles of high-speed, dangerous traffic. After leaving Elwood, we turned left onto Country Club road and had a respite from traffic and hills for a few miles. After this the climbs and rollers began as we approached PA-588 and continued to PA-989/ Glen Eden Rd which parallels the north side of I-76.
Leg 3: Down the hill from Cranberry Township to the Ohio River Valley at Ambridge.
Expected to be a high point of the route due to the long downhills, this was probably the most dangerous section. The plan was to use Brush Creek Rd and Big Sewickley Creek Rd to descend. Unfortunately there were no shoulders on this curvy, high speed road and this segment is NOT recommended. An alternate route using Camp Meeting Rd (includes a 1-mile 4% uphill) from Big Sewickley Creek Rd, then down via Fern Hollow and Little Sewickley Creek Roads would be safer.
Leg 4: Ambridge to the GAP
If the long hill to Ambridge is taken, you will want to turn left on Main, then left on Beaver Street to stay north of Route 65, which is dangerous in this area. Once in Sewickley, you can cross the bridge to a somewhat safer stretch of Route 51 (very unsafe north of here). Detour onto Neville Island at Coraopolis and emerge back onto 51 at the SE end of the island. If you want to begin the Great Allegheny Passage (GAP) at mile zero, Google Maps will direct you across the McKees Rocks Bridge, through a very big/busy intersection with 65 on the other side of the river, and up a hill into a neighborhood. Turn right on California Ave. Go left on Antrim, right on McClure, right on Ekert, right on Preble, and Left on Westhall to reach the Three Rivers Heritage Trail. From there you can access a bridge to "The Point" in Pittsburgh. The trail is relatively well-marked through Pittsburgh and It's outskirts to McKeesport. Much of the area is developed with the trail following shopping areas, etc.