What is system architecture? Why is it important in developing ITS?

Since the early 1990's many people have been advocating the use of stated ITS system architectures, indeed a number have already been created including the National ITS Architecture for the USA [ITS USA] and the European ITS Framework Architecture [Bossom 2000]. However, there is still a body of people who do not believe that they need their own system architecture, or that system architectures are not required at all. This is due, in part, to a lack of understanding of the issues involved. The paper covers five basic questions: When do we need a system architecture? What are the issues covered by a system architecture? What is a system architecture? What are the benefits of a system architecture? What is the European ITS Framework Architecture? (6 pages)