In reply to Martin W:
A friend of mine is a park ranger there, and the inside line is that there have been significant multi-ton rockfalls recently (around the great quarry) and more large unstable areas looking to drop. Historic Scotland are unable / unwilling to fund the full cleaning and stabilization work in the "foreseeable future" and so would rather leave the Radical Road closed. Its going to be years while they work it out.
The rangers themselves are no longer allowed to patrol the road due to the risk (they would normally do a daily sweep to check for folk fallen/jumped off the crags, but not anymore). Ironically its now more dangerous for people walking the clifftop than it was before the road was closed.
The upside of this scenario, is that nobody is going to be checking along the bottom to prevent you climbing in the south quarry. Also, the quarry can easily be accessed by down-climbing The Lift (M), but be sure you are able to identify the route correctly from above. Then you can play in the quarry bay without ever treading on the Radical Road.