If you are considering road travel in Thailand, it pays to know about this.
Consider it like “reading between the lines”–you don’t actually see the space between the yellow line down the center of the road, but it’s there, and Thais use it. I don’t mean like, “oh, there’s a long straightaway and I’ll pass the person(s) in front of me” or “I’m a motorcycle, so I’ll squeeze through” but rather like it’s actually a usable space by anyone willing to go head on with another user to see who compromises first; maybe akin to a street which is two-way but with too many cars parked on the street on both sides to you have to sidle down the street with other oncoming vehicles. Add to this the notion that there is no liscensing (that I know of) for drivers for special-sized vehicles (meaning it could be the first time the person has ever driven an 18-wheeler or not) and that many drivers are paid very little (meaning the faster they go, the longer their break) and you get the idea of who’s on the road.
It’s exciting, to say the least, and it made me glad that I brought a video-iPod so I could concentrate on something else visual and auditory. Oh, and I don’t recommend sitting in the front of the coach of buses (especially on double-deckers with the driver below you) or buses where the engine in the middle or back (a la VW buses).