Recently Intelligent Transport Systems (ITS) have acted as an efficient solution for improving the operational performance of traffic systems, reducing traffic congestion, and increasing safety for the travelers. But due to the inclusion of different distributed transport departments, heterogeneous devices, and diverse data sources, the architecture of ITS has become complex and costly. For an efficient and cost-effective architecture, ITS need to have easy and effective mechanisms for interacting among different transport subsystems. Recent technologies such as - service-oriented architectures (SOA), cloud or grid computing, provide a way of building a reliable and loosely-coupled distributed system. This paper surveys the promising solutions for distributed architectures of ITS and discusses opportunities and challenges in the context of ITS for public transport.