Managing the increasing traffic is a big problem all over the world. Intelligent Transportation System (ITS) provides solution to these problems with the help of new technologies. ITS is an integrated system that implements a broad range of communication, control, vehicle sensing and electronics technologies to solve and manage the traffic problems. ITS is being used in the developed countries since past two decades, but it is still a new concept when developing countries like India, Brazil, China, South Africa etc. are concerned. In the present study we have studied four major parts of the ITS i.e., Advanced Traveler Information System (ATIS), Advanced Traffic Management System (ATMS), Advanced Public Transportation System (APTS), and Emergency Management System (EMS). Objective of the paper is to study various ITS architecture and model and review such models to get in-depth of their architecture. Hence architecture and developed models over the years of four major branches of ITS have been reviewed here to make a comparison analysis of different models that have been developed by the researchers in their studies. It will lead to the gaps in the knowledge which can be further studied. The paper highlights the conclusions extracted from the studies of different systems and also gives the future scope in the field of ITS to make it more user friendly and accessible.