If you have a rental car you will have to be prepared for the fact that Thai drivers always jump red lights after dark. There is also a policy of the authorities following a highway collision to blame the foreign driver for causingthat collision~ their logic for this is " If you were not in the country the collision would not have happened!!" They also drive left hand drive cars ( like in the USA) on the left hand side of the road ( Like in the UK)
As for taxis, most drivers have a co-operstive and they will only take you to your destination and then wait for three hours to return you to your hotel. If you want less than 3 hours, or more than 3 hours then this charging schedule can be expensive.
Watch out for motor cycles, they nearly always have 5 people and a half ton load of produce on board!!!
I have to warn you about taxis and will post this in general. My husband and I have a business in the south of China and went to Thailand for "relaxation." We were convinced by a hotel employee to abandon our tourist bus to the destination and take a cab instead. A few hours into the ride, Mr. Mario Andretti decided to ramp it up to 85 mph without considering that he was boxed in and the red light was looming. I woke up to see our car flying through the air and landing in a gully after rolling several times. We were in the middle of nowhere, and there were no ambulances. We were thrown in the back of a pickup truck with no anesthesia or pain killers, which we desperately needed at that point. Initially, we were taken to a government hospital, which was a nightmare. NO one spoke English, and the facilities were archaic, to say the least. They took x-rays and told us we were fine (I think).
Finally, my husband was able to mutter something to the nurse who accompanied us in the truck and asked her to take us to Bangkok, which was hours away. She misunderstood and instead took us to one of a chain of private hospitals called Bangkok Hospitals about 2 miles away from the first hospital in a remote fishing village. This hospital was fantastic, but within 24 hours, they sent someone to our room to basically tell us that unless we put about $6K in cash down for deposit, we would be discharged. We were lucky to have our partner nearby in China, and he flew down with the 6 thousand dollar bills stuffed in his vest.
This was a shock for us, that our insurance basically covered nothing over there, as it was out of network. GET TRAVELER'S INSURANCE!!!!!!!! As I said, we were in a remote fishing village, but the place was so upscale we had access to internet, a plasma tv, and a kitchen in our room. We were there for 4 weeks, during which time there was a military coupe, flooding, some kind of terrorist bombing in the southern part of the country, and we had trouble being discharged and getting out.
Anyway, in the end, the cab driver turned out not to be licensed or registered, and he even tried to get us to give him some money for his injuries. Yeah, right. He nearly kills us, and he wants money.
A BIG CAUTION: Check the driver's credentials out in advance, WEAR YOUR SEAT BELTS (it is the only reason we are alive), and GET TRAVELER'S INSURANCE or make sure your policy will cover you. I cannot emphasize this enough.
P.S. Do not go to a government hospital. We were basically told there were no injuries over there, but when we got to the private hospital, we discovered that we were pretty badly injured ..... broken ribs, collapsed lungs, broken tail bones, and fractured vertebrae. NO CHEAP RIDE is worth what we went through. Please do your research ahead of time when choosing a driver. It is worth a few extra bucks and the time to check things out to prevent this kind of catastrophe.