I did a weekend trip this past August from Erie to Oil Creek State Park that worked well. Erie to Union City on Rte 97, then to Titusville via some back roads and Rte 8 - about 50 miles. Camped at one of the Adirondack shelters on the backpacking trail in Oil Creek SP. Saturday, I did a 65-mile round trip on roads and rail-trails south past Franklin & the Belmar bridge -- then camped at the second backpacking site. Sunday, returned to Erie via Rts 8 & 97. Didn't have to carry a tent because of the Adirondacks. Both backpacking sites have service roads (less than 1 mile each) that enable cyclists to access the campsites. I think the SP website says that only backpackers are allowed -- but I talked to one of the park rangers in advance and was told that it would be fine for a cyclist to use the service roads to get to those camps. The standard PA state park fees apply.
Check out the PA state bicycle routes.
BicyclePA Routes The portions that I've ridden generally have wide shoulders (except when passing through towns) and moderate traffic.
The only exception that I've encountered so far is a 15-mile section northeast of Pittsburgh on BikePA Route A from Coraopolis to Monaca on Rte 51. I cycled most of Route A with my son on a Washington DC to Erie trip this summer. (see our travelogue at
CrazyGuyOnABike).
Route 5 along Lake Erie is a nice ride. I've cycled most of the way from Erie to Buffalo on it and intend to do a weekend camping trip to Evangola State Park in NY -- about a 70 mile one-way trip for me.
Hope this helps...