Please be advised that that site includes "roads" that are closed off to vehicle traffic but still open to bicycling and hiking (for example, it shows the 180+ length of the C&O Canal towpath). I think it is actually more intended for gravel cyclists.
Awesome!! Thank you Vince!!
These work good for emergency evacuation routes too!
I have used many a 'hidden' gravel road to make rescues. I used to have to call the local fire department for information.