Here’s another route that I’ve considered using, but HAVE NOT field verified….. It would take you from West Jeannette to the GAP at Boston. Trail could then be used to take you into South Side, with caution used in vicinity of Sandcastle/Glenwood Bridge.
You didn’t mention buses, but I’ll throw out the info anyway. If you can make it from Jeannette to Trafford, you can catch a 69 to Oakland, then hop off & go down the Panther Hollow Trail to Jail Trail to Hot Metal Bridge. All the buses have racks now, and the 69 runs every half hour.
Swalforts link did the trick, I think. This is actually for a co-worker. Might ride the route with him one of these days. It will be ~25 miles one way but it seems like if a good pace is kept it won’t be much longer considering how the parkway can crawl at times.