Coaches [are only allowed] one-way Beauvoir to NOIRMOUTIER.
Why are coaches only allowed one way Beauvoir to Noirmoutier on the Passage du Gois?
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The hide tide submerges the 4-kilometer-long Passage du Gois twice a day, making it a very special road. The road goes from Beauvoir on the continent (East) to the island of Nourmoutier (West) and crosses the Bourgneuf bay. There a current flowing from the North to the South toward the Goulet de Fromentine.
The current tends to remove or deposit sediments depending on whether it slows down, accelerates... It triggers an erosion on the Southern side of the road . In the linked article, there is a picture of a 1 meter step between the road level and the sediment level. The paving the road created a dregding channel on its southern side that threaten its stability. Quoting the article:
Au contraire, la vitesse du flot venant du nord étantélevée, le côté sud de la chaussée prend l’allured’une petite cascade
On the contrary, the speed of the flow coming from the north is so high that the southern side of the road looks like a small waterfall.
This scouring phenomenon endangers the road, and the authorities have likely decided to reduce the loads and risks on this side of the road. Heavy trucks and coaches are therefore forbidden on the southern side of the road. As french people drives on the right side of the road, coaches are only allowed from Beauvoir (East) to Noirmoutier (West).
L'évolution historique du passage du Gois du 18ème siècle à nos jours