The section around Barbury Castle and Hackpen Hill is closed - and the line has been re-routed onto tarmac. Smeathes Ridge towards Ogbourne is also closed. The seasonal TRO sections on other sections opens up after 31st April each year. Again, I would say don't bother with the Ridgeway - too busy and boring.
There are some very good alternative lanes around there without using the Ridgeway such as Ogbourne Maizey to Barbury and around Aldbourne. Just get a map, the roads are well posted and enjoy.