As regular as rush hour.. formation late afternoon, then pour around 5-7pm. Massive traffic jam everywhere. Maybe it's nature a way of saying enough with the cars and pollution!?
"Bangkok presently adds about 600 new cars daily to the traffic stream which equates to an extra 3 km of bumper-to-bumper traffic. At this rate in less than 4 years enough cars are added to fill the entire road system with one lane of traffic."
"Bangkok is shown to have a very high density, mixed use urban form with low provision of roads, in common with other Asian cities, but with very high parking provision in the CBD. It has high vehicle ownership and use for its relatively low level of wealth and much new development is building in automobile dependence. Use of public transport is similar to that in European cities, though it is not high when compared to many other Asian cities. The environment for walking and cycling is very hostile and use of these modes is abnormally low for an Asian city. Detailed studies of air pollution show that for Bangkok to reduce its severe air pollution problem it will need to not only adopt the best technology available, but will require more transport infrastructure projects than currently committed, especially a rail system, and demand management measures to curtail growth in traffic. "
Read more "detailed comparison of Bangkok's land use and transport system characteristics with cities in North America, Europe and Australia and in particular, other Asian cities such as Kuala Lumpur, Jakarta, Manila, Seoul, Surabaya, Singapore, Hong Kong and Tokyo."