In this video i found something interesting, someone do something like : Drifting in a drag race area etc. Now play the video and see. You will look a "unknown" race track, which not appears in bayview (After a minutes ago, you will see). In my guess, The 2 unknown tracks in the video is driveable area, but dont know how to go there.
Plus, the unknown tracks , maybe it's unfinished tracks, also, i think it was cut track.