I received word two days ago that the Success Pond Road is blocked off by boulders at both ends. Is this a fact? Hopefully someone knows, or can check. I am a bit far away to see myself.
Also, it does get temporarily blocked by boulders every spring for mud season, so sometimes when people search the 'net for information on Success Pond Road they find the announcement of that closure.
I drove in from Berlin yesterday - went through the Mahoosuc Notch and back down. Completely accessible. (We did not try to go out the Grafton Notch end.)