This question is based on a real world scenario…
There is a causeway, roughly 1/4 of a mile long, over which the tide rapidly rises twice a day, rendering the tourist hot spot at the wrong end of it cut off from the rest of the country for several hours at a time.
Every year there are numerous incidents of cars caught out, in the middle of the causeway, occupants on the roof, awaiting expensive rescue.
There are warning signs, but as we know warning signs are often not heeded and anyway, these signs simply say 'check the times' and barriers would not work as there is plenty of flat sand around the causeway
There is also a problem with people running late, who know the time but can't afford to be stuck for hours waiting for the causeway to become passable again
The question is this:
How can a causeway and its surrounding environment be altered in such a way as to ensure that as few people as possible are caught and left requiring expensive rescue?