I don't know about any "road", but up in that area it's very dangerous to run the shoreline at night when trying to get your bearings... there's a number of old dock remains (petrified pilings) that reach quite a ways out into the bay. They're just below the water now and none are marked (they're on charts).
If you look closely at the end of Marsac Creek there is a shallow area that could have been a road, many years ago.
Checking old records at the local library could give up some info. There were a lot of old logging roads nearby that area, but that was some time ago.
My dad has been in the area since 1936 and is not familiar with a road like you describe.
At the end of the canals near The Sandbar, used to be called The Piers, there were a few more houses that are no longer there. Apparently there used to be a dance hall or barn at the end of the road where The Sandbar now is. The old timers around here will tell you of a dance floor sunken out there.
I did a quick search on the sunken road and I got sidetracked with the following. I will be treasure hunting shortly. I hope the ghost doesn't get me.
A settlement was made as appears by a Captain Francois Marsac in about 1798, at Tremble Creek, the stream near New Baltimore, on the Ridge Road, and also prior to 1796, at Swan Creek, some four miles west of New Baltimore.
From the early settlement of that section a tradition has been handed down, and this tradition has many believers even now, that an English Captain or Lieutenant, who had been largely successful in gathering together a quantity of bullion, being compelled to flee from the Indians, buried his treasure in the earth, about a mile from the present isle of New Baltimore, that he was either killed by the Indians, or died from exposure, and the secret of his treasure's hiding place died with him. Many searches have been made by infatuated individuals after this treasure, and many believe that the ghostly shade of the deceased Captain guards the treasure-trove so jealously, and has such power of moving its location, that all search is in vain.