Read all about it here https://www.crazyguyonabike.com/doc/?o=tS&doc_id=9422&v=Gw
I highly recommend that you not
use Bike 5 between Schenectady and Albany. There is little lane space and lots of traffic. Instead, use the Mohawk-Hudson trail, part of the Canalway Trail system. I also recommend that you not use Bike 5 through Rochester; again, no lane space and heavy traffic. The canal trail across Rochester is paved and a nice ride.
The canal trail is largely unpaved but improved, typically rolled stone dust. The paved parts are the Mohawk-Hudson Trail, a stretch near Canajoharie, through Rochester and through Buffalo. There are a few other places that are paved.
Get the Parks & Trails guide, for all the info on the trail parts. Yes, the trail can be a challenge to follow in places.
You need to decide if you're going to go through Syracuse or around it to the north. Going through is ok using the route in the guide book. The advantages are that you can use the Old Erie Canal on the east, and the best canal museum is downtown.
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