I heard that there are two possibilities to get to the island of Noirmoutier. You can either use a bridge, or you can use a pass through the water, which is only drivable if the tide is low. Is this dangerous to cross? And what if I'm stuck halfway? Is there an emergency service?
Passage du Gois is a natural passage with a length of 4,3km (2.58-miles), located in the Atlantic coast of France in the Vendée. Part of the D948 leading to the island of Noirmoutier floods with high tide, and is accessible only during low tide, 1½ hours each before and after the lowest tide. If you miscalculate, there are refuge markers which you would have to climb; your vehicle is another matter.
For safety, the current time and the time of the next low tide are indicated at the entrance.
Great images courtesy of Dangerous Roads and Les Mouettes 17.
If you make it across safely, and dry, splurge on a meal at La Marine, Alexandre Couillon's Michelin-starred restaurant.
Is this dangerous to cross?
As you can see on Wikipedia, fatalities are very rare, fewer than one every few years. https://www.passagedugois.com/crbst_3.html gives some tips to avoid sinking your car and some current information (tide, weather, etc.).
Keep in mind that the area is very flat: as a result, if the tide is going up and that you see some water coming and/or you see many more cars exiting the pass than entering it, double-check the tide times. If the weather is already on the road, unless you are extremely sure about yourself, don't enter the road.
There are two possibilities to get to the island of Noirmoutier