I did a search on Success Pond road and didnt get much of a response so I figured it was time to right this.

Success Pond Road accesses several trail heads on the north side of the Mahoosuc range on the Maine NH border. It is a logging road that has been in place for many years. There are zero services on this road and at most there are a couple of seasonal hunting shacks and cluster of camps around Success Pond. There is also no cell service along much of it. There is occasional traffic on the road but there is no longer much active logging as the prior owner of much of the land stripped it clean. So in an emergency it is definitely a poor choice for an escape route. as dependent on the trailhead used it may be 12 mile walk to civilization in Berlin NH or a much longer walk out to RT 26 in Maine. Shuttle services will deliver hikers along the road but the cost is generally high as the slow speed and poor condition means pay per mile just does not cover the driver's time. Given the lack of cell coverage getting a ride from a trailhead on the road is nearly impossible unless the shuttle firm was contacted up on the ridgeline in advance.

The road is maintained for logging trucks and may be closed during spring "mud season". In winter it may be maintained for logging operations but do not plan on it. The traditional advice for passenger cars driving on it is plan in 20 MPH average. Some locals drive far faster and in some sections the road is quite curvy so keep an eye out. I recently drove up the road while doing some trail magic for section hiker who didnt plan very well. The road is better condition than in the past. It is still rough in many places and better suited for logging trucks but with a bit of care any passenger vehicle should be able to drive it.