Train
The State Railway of Thailand offers train services throughout the country at very reasonable fares. Most long-distance trains start off from Bangkok's Hualamphong Station on Rama IV Road. The four main rail lines, covering over 4,000 km., are the northern, northeastern, eastern and southern routes. Note that the trains to the northern and northeastern routes pass Don Muang airport station, so you can catch a train here if you go to any province along either route to avoid heavy traffic in town in rush hours.
There are four types of trains -- ordinary, rapid, express and special express, and three classes of cars -- 1st, 2nd and 3rd.
For a long distance trip, the fare for the 2nd class is about the same as a private tour bus, but some say that the train is more comfortable, especially on overnight trips. However, travelling by train take a bit longer than by bus.