The National ITS Architecture: a framework for ITS Structure

Public Roads, Sept-Oct, 1997 by Lee Simmons

Over the past decade, as information- and computer-based systems have become larger and more complex, the importance of and reliance on systems architectures have grown substantially. A systems architecture is the framework that guides and moderates the evolution of a complex system's many interrelated elements. It provides order and rules so that hardware, software, data, and communications can work together.

"Systems architectures have emerged as the centerpieces of system development programs," notes the General Accounting Office.

The centerpiece of intelligent transportation system (ITS) development is the National ITS Architecture - a systems architecture developed by a combined Lockheed Martin and Rockwell International team (representing the public sector, private sector, and academia) for the U.S. Department of Transportation (DOT). The architecture was completed in June 1996, after nearly three years of effort, including more than 50 stakeholder meetings, briefings, and workshops.

The architecture's development has been an important first step toward achieving the DOT's goal of encouraging states and localities to build an intelligent transportation infrastructure in metropolitan and rural areas, as well as interstate corridors. Without a systems architecture, ITS deployment would be analogous to states, cities, and counties each building small parts of a limited-access freeway with little regard for its connections to segments in other jurisdictions. The National ITS Architecture shows how individual ITS services can be linked together to create intermodal and interoperable systems that better serve travelers and system managers in all areas. The architecture achieves three specific objectives:

* Provides a theoretical and practical framework in which 30 ITS services can operate together to provide various levels of service to travelers and system operators.

* Illustrates how ITS services can be incorporated within an existing infrastructure and can accommodate future technological advances.

* Supports "open" standards that enable multiple public- and private-sector organizations to independently deploy ITS components that work together, regardless of who designed or manufactured the particular hardware or software.

The architecture is quite extensive and contains more than 5,200 pages of documentation in 18 volumes. It is also the world's first systems architecture for ITS development and deployment.

A Framework for Building ITS Infrastructure

Any complex system that consists of many technical components and subelements carries the inherent risk of technological chaos - incompatibility, premature obsolescence, costly inefficiency. A system architecture provides a unifying framework to ensure that technologies can work together smoothly and effectively. The system architecture for a home entertainment system, for example, allows a television, videocassette recorder, audiotape deck, compact disc player, radio, headphones, speakers, and remote control, as well as future add-ons, to function as a unified system, even when individual components are designed and produced by different manufacturers.

In much the same way, the National ITS Architecture defines major ITS components and describes how system elements can interact compatibly. It provides a comprehensive technical and institutional framework that allows individual ITS services and technologies to work together and share information. More specifically, the architecture defines the following aspects of ITS infrastructure:

* Functions necessary to perform a given ITS service.

* Subsystems that enable ITS services to function (e.g., roadway or transit management center).

* Interfaces and information flows between subsystems.

* Wired or wireless communication modes available for transmitting ITS information.

* Requirements for developing standards to support national ITS interoperability.

The ITS architecture consists of a logical architecture and a physical architecture. The logical architecture defines eight major processes and associated information flows: (1) managing traffic, (2) managing commercial vehicles, (3) providing vehicle monitoring and control, (4) managing transit, (5) managing emergency services, (6) providing driver and traveler services, (7) providing electronic payment services, and (8) planning system deployment and implementation.

The physical architecture allocates the processes of the logical architecture to 19 major physical subsystems that are organized into four basic physical classes: transportation management centers, roadside equipment, vehicles, and travelers.

The physical architecture addresses three major layers of infrastructure: transportation, communications, and institutional. The transportation layer deals with the transportation infrastructure and operations of ITS. The communications layer identifies how existing and developing commercial or dedicated communications systems and open protocols can support ITS services. And the institutional layer outlines possible roles and relationships among public and private institutions - particularly how the federal government, state and local governments, vehicle manufacturers, and information and communications service providers could work together to implement ITS services.