There are numerous traffic lights in Bangkok city and the lights changes very quickly and before you knew it, it's red light again and that seems to be the main cause of the traffic jams in Bangkok. The green is on for one direction at a time and this can cause a quick traffic build up and thus the famous traffic jam.
If you think that it just normal traffic jam, then you can be very surprised.
A 2 hour traffic jam can be the norm.
Initially, I told the taxi driver to take me to the hotel. Seeing that the traffic is not moving, I changed my mind and asked him to take me to Skytrain's National Stadium station. Again, the traffic didn't move much. He diverted and we decided on Hua Lamphong MRT station which we, ultimately, make it there after an hour. All this time, I had my pda GPS on and could see clearly whether he is taking any longer route unnecessary. Conclusion, taxi drivers are alright.
If you think you can take the BTS and MRT to avoid the traffic jam, you may be in for a surprise where the BTS only runs through a section of the city and miss the main tourist spots like the Wat Pharaew/Grand Palace, Wat Pho, etc.
Bangkok has the worst traffic problems ANYWHERE! If you don't like traffic jams, do not come to Bangkok - it's hell. I'm from Toronto, Canada and I simply didn't know it was possible for cities to be so poorly organized regarding traffic. I've spent hours stuck in traffic to get distances that you could walk in an hour or so - IF it wasn't so freaking polluted and hot. One example - there is lots of construction here and they still use asbestos in the concrete and you can get huge lung fulls of the stuff just walking a couple blocks past a couple of sites. That's not even talking about all the other background pollutants. (My nose used to sting just being on a busy street - not now, those nerves having died off I presume.)
Many bangkok Taxis are metered but if you want to cacth a flight in the middle of rush hour 4PM to 8PM, you can consider to catch a taxi without meter, bargain and drive.
I once get a cab from MBK to Airport for THB with a hard 50% bargain. I tried to find a "sport" driver and the result was 45 minutes back to Airport compared to 75 minute when I came from airport.
he'll find best route for u. just sit down, fasten your seat belt and "relax" ;-)
But you should know exactly the cost of taxi meter on the same route before. For comparison, Airport to MBK on meter was around USD 11, for non metered taxi + faster was around USD 15.
As you can see from the photo, there is no need to check what speed you are doing around Bangkok because it is usually zero anyway!