+1 surly jason
There is a large, primarily unused park-and-ride lot under PA65 by Island/Beaver/Chateau/California/Marshall. Park car there, and then it's an easy ride to the river trail.
jimmy, I'm north, too, but directly north, about 10 miles. When I bike the entire way in, I use either Babcock Blvd into Millvale, or PerryHwy to West View, Center over to Bellevue, cross the open-only-to-peds-and-bikes bridge, L Benton, wiggle over to Shadeland and eventually Brighton, and further wiggle over to the FtDuqBridge. Fairly flat, fairly light traffic.
PM me if you are near one of these paths, and up for a ride into the city together sometime.