By Road

Thailand's roads are head and shoulders above its neighbors Myanmar, Laos and Cambodia, but driving habits are still quite dangerous. Drunk driving, speeding and reckless passing are depressingly common, and bus and taxi drivers (especially for private companies) work inhuman shifts and often take drugs to keep themselves awake, with predictable and tragic results. It's common for motorbikes — even police! — to drive close to the curb on the wrong side of the road. Death tolls sky-rocket around major holidays, especially Songkhran, when bystanders often throw water on passing cars and bikes. Many drivers don't use headlights at night, multiplying risks, and it is wise to avoid or minimize overnight travel by road.
Note that unlike in its neighbours (except Malaysia), traffic moves on the left side of the road in Thailand and Thai cars are generally right-hand drive. All official road directional signs are written in both Thai and English.

Bus
Buses travel throughout the country and the government's bus company BKS (Baw Kaw Saw), known in English simply as the Transport Company, has a terminal in every province of any size.

Generally speaking, BKS buses are the best option for both price and comfort. There are also private buses sanctioned by BKS, which operate on the same routes from the same terminals with the same fares, and these are also fine. The basic BKS bus types are:
Local - relatively slow, can be cramped when full (nevertheless there's always room for one more), and stop at every village and cowshed along the way. Many are of larger songthaew flavour. Not suitable for long-distance travel, but may be the only cheap way to get around locally.

Express (rot duan) - skip some stops, but no other frills. Identifiable by their orange colour. Size varies, with the largest having around 65 seats (five seats per row) as well as an open space across the width of the bus by the back door for you to sling your backpack, bicycle, sack of rice, live chickens, etc.

Second class (chan song) - skip more stops, but often take a less direct route than 1st class / VIP / S-VIP. Blue and white with an orange stripe, usually 45-48 seats per bus, air conditioned (some provide blankets, some do not). Most have no on-board toilet, although the frequent stops mean this isn't a problem.

First class (chan neung) - generally take the most direct routes and make very few stops. Blue and white in colour, air conditioned, blanket usually provided, fewer (larger, longer pitch) seats (typically 40, but some double-decker types seat 60+), snack and drinking water included. Toilet on board for all but the shortest services.
"VIP" - as per 1st class, but with only 32-34 seats, which have more leg room and recline further. Basic meal included and freshly laundered shrink-wrapped blanket provided. Also blue and white (or sometimes blue and silver) but usually signed "VIP".
"S-VIP" - Super-VIP is very similar to VIP, except there are only 24 seats, which are wider - the aisle is offset, each row having a pair of seats on the right and only a single seat on the left. Primarily used on overnight services.

Some buses may have TVs and sound systems blaring, so earplugs are well worth having, just in case. On long-haul buses, if your ticket allocates you a front seat, you may have to switch seats if a monk boards.

Songthaew
A songthaew is a truck-based vehicle with a pair of bench seats in the back, one on either side — hence the name, which means "two rows" in Thai. In English tourist literature, they're occasionally called "minibuses". By far the most common type is based on a pick-up truck and has a roof and open sides. Larger types start life as small lorries, and may have windows, and an additional central bench; smaller types are converted micro-vans, with a front bench facing backwards and a rear bench facing forwards.
Songthaews are operated extensively as local buses (generally the most economical way to travel shorter distances) and also as taxis; sometimes the same vehicle will be used for both. Be careful if asking a songthaew to take you to someplace if there is nobody in the back, the driver might charge you the taxi price. In this case, check the price of the ride before embarking.

Tuk-tuk
The name tuk-tuk is used to describe a wide variety of small/lightweight vehicles. The vast majority have three wheels; some are entirely purpose-built (eg the ubiquitous Bangkok tuk-tuk), others are partially based on motorcycle components (primarily engines, steering, front suspension, fuel tank, drivers seat). A relatively recent development is the four wheeled tuk-tuk (basically a microvan-songthaew) as found in Phuket.

Taxi
Metered taxis are ubiquitous in Bangkok and starting to become more popular in Chiang Mai, but rare elsewhere in the country. When available, they are an excellent means of transport - insist on the meter. Beware of taxis which idle around touristy areas and wait for people. They are looking for a tourist who will take their taxi without using a meter. Always use the meter.

Motorbike
As is the case throughout virtually all of Asia, motorcycles (motosai) are the most common form of transport overall; the most popular type are the 100cc-125cc step-through models. These are very widely used as taxis, with fares starting from as low as 10 baht. Negotiat the fare to the driver before use his service protect he charges you too high.

Motorcycles can be rented without difficulty in many locations. Rates start at around 150 baht/day for recent 100-125cc semi-automatic (foot operated gearchange, automatic clutch) step-through models, 200 baht/day for fully automatic scooters.
Insurance is usually not included (or even available), so try to ensure in advance that the insurance you leave home with is going to cover you; alternatively, arrange cover with an insurance broker locally in Thailand. If you rent a vehicle without insurance and it's damaged or stolen, the bottom line is that you will be required to pay in full the cost of repairing or replacing it. Furthermore, some travel insurance policies will only provide medical cover in the event of an accident if you hold a motorcycle license in your home country.

Some (but not all) border crossings allow motorcycles through. At those which do, documentation including proof of ownership must be produced (with the possible exception of day visits to Payathonzu, Myanmar via Three Pagodas Pass).

Rental car

Driving your own car in Thailand is not for the faint-hearted, and many rental companies can supply drivers at a very reasonable price. Prices without insurance for a self-driven car start from around 800 baht/day for small cars, and from as little as 600 baht/day for open-top jeeps; cars with insurance start at just under 1000 baht/day, and come down to around 5600 baht/week or 18000 baht/month.

Driving is on the left hand side of the road. As of June 2008, fuel at large petrol stations is 37-41 baht/litre. Small kerbside vendors who pump by hand from drums and/or pour from bottles charge a few baht more.

More reputable agencies require that valid licences be produced: foreigners who do not have a Thai driving licence must carry a valid International Driving Permit. Even if you manage to rent a car without an IDP, not having one will invalidate the insurance and count against you in the event of an accident.

A common rental scam involves the owner taking a deposit, and then later refusing to refund it in full on the basis that the customer is responsible for previous damage; the Tourist Police (dial 1155) may be able to help. Another common scam involves the owner having someone follow the rented vehicle and later "steal" it, using a set of spare keys. Always report thefts: a "stolen" vehicle may mysteriously turn up as soon as the police become involved.

Thailand's roads are head and shoulders above its neighbors Myanmar, Laos and Cambodia, but driving habits are still quite dangerous. Drunk driving, speeding and reckless passing are depressingly common, and bus and taxi drivers (especially for private companies) work inhuman shifts and often take drugs to keep themselves awake, with predictable and tragic results. It's common for motorbikes — even police! — to drive close to the curb on the wrong side of the road. Death tolls sky-rocket around major holidays, especially Songkhran, when bystanders often throw water on passing cars and bikes. Many drivers don't use headlights at night, multiplying risks, and it is wise to avoid or minimize overnight travel by road.
Note that unlike in its neighbours (except Malaysia), traffic moves on the left side of the road in Thailand and Thai cars are generally right-hand drive. All official road directional signs are written in both Thai and English.

Bus
Buses travel throughout the country and the government's bus company BKS (Baw Kaw Saw), known in English simply as the Transport Company, has a terminal in every province of any size.

Generally speaking, BKS buses are the best option for both price and comfort. There are also private buses sanctioned by BKS, which operate on the same routes from the same terminals with the same fares, and these are also fine. The basic BKS bus types are:
Local - relatively slow, can be cramped when full (nevertheless there's always room for one more), and stop at every village and cowshed along the way. Many are of larger songthaew flavour. Not suitable for long-distance travel, but may be the only cheap way to get around locally.

Express (rot duan) - skip some stops, but no other frills. Identifiable by their orange colour. Size varies, with the largest having around 65 seats (five seats per row) as well as an open space across the width of the bus by the back door for you to sling your backpack, bicycle, sack of rice, live chickens, etc.

Second class (chan song) - skip more stops, but often take a less direct route than 1st class / VIP / S-VIP. Blue and white with an orange stripe, usually 45-48 seats per bus, air conditioned (some provide blankets, some do not). Most have no on-board toilet, although the frequent stops mean this isn't a problem.

First class (chan neung) - generally take the most direct routes and make very few stops. Blue and white in colour, air conditioned, blanket usually provided, fewer (larger, longer pitch) seats (typically 40, but some double-decker types seat 60+), snack and drinking water included. Toilet on board for all but the shortest services.
"VIP" - as per 1st class, but with only 32-34 seats, which have more leg room and recline further. Basic meal included and freshly laundered shrink-wrapped blanket provided. Also blue and white (or sometimes blue and silver) but usually signed "VIP".
"S-VIP" - Super-VIP is very similar to VIP, except there are only 24 seats, which are wider - the aisle is offset, each row having a pair of seats on the right and only a single seat on the left. Primarily used on overnight services.

Some buses may have TVs and sound systems blaring, so earplugs are well worth having, just in case. On long-haul buses, if your ticket allocates you a front seat, you may have to switch seats if a monk boards.

Songthaew
A songthaew is a truck-based vehicle with a pair of bench seats in the back, one on either side — hence the name, which means "two rows" in Thai. In English tourist literature, they're occasionally called "minibuses". By far the most common type is based on a pick-up truck and has a roof and open sides. Larger types start life as small lorries, and may have windows, and an additional central bench; smaller types are converted micro-vans, with a front bench facing backwards and a rear bench facing forwards.
Songthaews are operated extensively as local buses (generally the most economical way to travel shorter distances) and also as taxis; sometimes the same vehicle will be used for both. Be careful if asking a songthaew to take you to someplace if there is nobody in the back, the driver might charge you the taxi price. In this case, check the price of the ride before embarking.

Tuk-tuk
The name tuk-tuk is used to describe a wide variety of small/lightweight vehicles. The vast majority have three wheels; some are entirely purpose-built (eg the ubiquitous Bangkok tuk-tuk), others are partially based on motorcycle components (primarily engines, steering, front suspension, fuel tank, drivers seat). A relatively recent development is the four wheeled tuk-tuk (basically a microvan-songthaew) as found in Phuket.

Taxi
Metered taxis are ubiquitous in Bangkok and starting to become more popular in Chiang Mai, but rare elsewhere in the country. When available, they are an excellent means of transport - insist on the meter. Beware of taxis which idle around touristy areas and wait for people. They are looking for a tourist who will take their taxi without using a meter. Always use the meter.

Motorbike
As is the case throughout virtually all of Asia, motorcycles (motosai) are the most common form of transport overall; the most popular type are the 100cc-125cc step-through models. These are very widely used as taxis, with fares starting from as low as 10 baht. Negotiat the fare to the driver before use his service protect he charges you too high.

Motorcycles can be rented without difficulty in many locations. Rates start at around 150 baht/day for recent 100-125cc semi-automatic (foot operated gearchange, automatic clutch) step-through models, 200 baht/day for fully automatic scooters.
Insurance is usually not included (or even available), so try to ensure in advance that the insurance you leave home with is going to cover you; alternatively, arrange cover with an insurance broker locally in Thailand. If you rent a vehicle without insurance and it's damaged or stolen, the bottom line is that you will be required to pay in full the cost of repairing or replacing it. Furthermore, some travel insurance policies will only provide medical cover in the event of an accident if you hold a motorcycle license in your home country.

Some (but not all) border crossings allow motorcycles through. At those which do, documentation including proof of ownership must be produced (with the possible exception of day visits to Payathonzu, Myanmar via Three Pagodas Pass).

Rental car

Driving your own car in Thailand is not for the faint-hearted, and many rental companies can supply drivers at a very reasonable price. Prices without insurance for a self-driven car start from around 800 baht/day for small cars, and from as little as 600 baht/day for open-top jeeps; cars with insurance start at just under 1000 baht/day, and come down to around 5600 baht/week or 18000 baht/month.

Driving is on the left hand side of the road. As of June 2008, fuel at large petrol stations is 37-41 baht/litre. Small kerbside vendors who pump by hand from drums and/or pour from bottles charge a few baht more.

More reputable agencies require that valid licences be produced: foreigners who do not have a Thai driving licence must carry a valid International Driving Permit. Even if you manage to rent a car without an IDP, not having one will invalidate the insurance and count against you in the event of an accident.

A common rental scam involves the owner taking a deposit, and then later refusing to refund it in full on the basis that the customer is responsible for previous damage; the Tourist Police (dial 1155) may be able to help. Another common scam involves the owner having someone follow the rented vehicle and later "steal" it, using a set of spare keys. Always report thefts: a "stolen" vehicle may mysteriously turn up as soon as the police become involved.