The first, and probably easiest, has you leave the current route at St Augustine (if you are going north) and head over toward Green Cove Springs on SR 16/SR13, then up the east coast of Lake George and the St Johns River on Madrid Ave. This is shown as a high traffic road on our Bicycle Friendly Roads app, but it is the preferred route of the local cycling club. I expect they are using it during off-peak traffic times, and apparently folks on this route are used to seeing cyclists.
You cross into downtown Jacksonville on the Acosta Bridge, then take Main Street/US 17 north to rejoin the existing bike routes. Main Street/US 17 is a multilane road, and there are bike lanes north of the railroad tracks (we need to reflect this on the website) but not south of the RR tracks. Cyclists can take the outside lane, or they could use one of the smaller parallel residential streets instead (that’s what I’d probably do.) You can see these on the website.
The second alternative would be to continue north to US 90/Beach Blvd, due east of Jacksonville, and ride that west toward Jacksonville. US 90 has spotty bike lanes most of the way in, but as you get close to town you’ll want to jump off onto the local grid and connect to the Acosta Bridge, then it’s north on 17 as described above.
The website he is referring to is their Bicycle Friendly Roads interactive map found here: http://www.dot.state.fl.us/rddesign/BikeRouteViewer/