For those who don't read Thai, the proper translation would be:
"Cutting across lanes to u-turn causes accidents and is illegal.
(U-turns should be made at the next opportunity)"
Even the Thai doesn't state where that opportunity is...
For those who don't read Thai, the proper translation would be (note, the name of the beach is Haad Sai Keaw, which means Glass Sand Beach):
"Last public transport service to/from Haad Sai Keaw is at 18:00.
From 17:00 you are allowed to bring your own vehicle to the beach."
Well, would you have figured that out?