if you had studied phonetic for english when you were little, you may (or may not) notice that all the english names on road signs and government publications are written in a slight different way than what we used to know in phonetic pronunciation. if you don’t know the official transcription you might wonder why “คลองเตย” is written as “khlong toei” instead of “klong toei” or “phra ram 9” is actually pronounced as “pra ram nine” not “fa ram nine” or “จตุจักร” is supposed to be written as “chatuchak” not “jatujak

those signs and publication were written according to the royal thai general system of transcription (RTGS) which is the official system for rendering thai in the latin alphabet. this transciption was created to diffrentiate thai alphabets, though this transciption does not record the tone which a word should be pronounced (in thai language, a word with a different tone has a different meaning). short and long vowels are impossible to differentiate with this transcription either.

if you want to know more about how to romanize thai alphabets, you may visit thai royal institute (ราชบัณฑิตยสถาน) // principles of romanization is also available in pdf format.