Its easy, we have a few roads here like that,
Look on the google link you posted, next to the lane you will see a set of gates (dead give away) pan out, then follow the track you can see, it heads straight into the woods to the dual carriageway, at that point the carriageway intersects the lane/old road, they layout tells the story
Moor Lane and Folkes Lane used to be one connected road before the road to the M25 was built.
The council when they built the carriageway had get a TRO leading to a Permanent Restriction then when work on the road ceased it was down graded to a restricted byway.
Many carriageways and motorways have wooded areas around them and need access for maintenance, hence the gates on what would have been an old road and the pedestrian access that is now the restricted byway
