Famous submersible road unique in Europe (and perhaps in the world) 4.5 km long. This portion of the D948 is discovered at low tide. You can cross it without any problem 1h30 before the low tide schedule, and until 1h30 after. Consult the schedule and the tidal coefficient to prepare your passage. There may possibly remain pockets of water on the road at the ends of this time window and / or during a low tide or when the weather is rough.
The coating consists of a succession of portions of bitumen, paving stones or concrete slabs. There are significant holes in the pavement, especially in the paved sections, so be careful where you put the wheels. You should also know that the road is cleaned daily, including algae, by the DDE; it is therefore relatively clean.
Finally, the Passage du Gois suffered somewhat from its success. There can be heavy car traffic during summer holidays and bridges, and also on high tide days. In my opinion, one day it will be necessary to consider limiting the circulation of vehicles, or quite simply applying the legislation which normally prohibits cars from parking on the side of the road; for now, tolerance remains the rule in this regard.