The more I read this thread the more I become convinced that the posts are made by Sunday drivers. The only time I have ever been bothered sitting in a vehicle in Thailand, is the taxi from the airport. Once upon the toll road, most of them seem intent on dropping the engine out of the taxi (due to high speed and engine strain). The van and bus drivers have always seemed to be careful and knowledgeable. Remember one who seemd to know every shortcut in Bangkok when going from hotel to hotel picking up passengers avoiding the early morning traffic. Perhaps it depends on the tour operators, the cheaper you go, the less careful drivers they employ!