I was on the Suvarnaphumi - Hua Hin bus last night.
Within 30 or so km to the accident site, traffic is in gridlock and a section that usually takes about 15 minutes took 45.
BUT,once past the site, the bus, to make up the lost time, revved up and shot like a bat out of hell, and my wife and I were scared $hitless.
Like most of us on this thread, I have come across dangerous situations on the roads of Thailand many times before. But last night we truly feared for our lives.
BE WARNED, take the train (or as KhunLA says above, take Highway $4).