The needs expected to be fulfilled by AHS have been organized here and the functions and the performances expected of the principal user services have been classified as "requirements". The logical architecture has been designed according to this and the functions and related items to be realized by each service have been systematized by constructing a function structure diagram.

Each function set with the logical architecture has been assigned a physical class such as onboard device, roadside facility, etc., and a physical architecture that systematizes function assignments, information exchanges, and information exchange timing among each class was designed.

On this physical architecture, by overlapping the expected performances of quantity services set by the requirements, the target performance for each physical class (device) was set and expected specifications for technology were set as demanded performances per device.

From Logical Architecture to Physical Architecture
We placed "function" on the diagram of the physical class and clarified the locations where functions will be realized.

The contents of the information flowing among the physical classes set on the horizontal axis were plotted on the message tracing diagram. Furthermore, the demanded performances from the requirements expected of the system will be distributed as time performances.
By doing this, the demanded performances of for each physical class (device or technology) will be set.

In setting the physical architecture, when realizing the principal user services of "improving safety" and "improving efficiency and the environment", mutual checks between each user service are necessary. In the future, for assigning road-to-vehicle communication, it is necessary to coordinate functions of ITS in its entirety through discussion and coordination with the Advanced Safety Vehicle (ASV) project responsible for research on vehicles.

In the requirement specifications of the element technologies, based on required performance systematizing functions of technology based on the type of road and the segment of road, development of each technology is being carried out through work assigned within AHSRA.