National ITS Architecture Glossary

Subsystems that provide management, administrative, and support functions for the transportation system. The center subsystems each communicate with other centers to enable coordination between modes and across jurisdictions. Some examples of center subsystems are Traffic Management, Transit Management, Commercial Vehicle Administration, Archived Data Management, Emissions Management, Toll Administration, Emergency Management, Information Service Provider, and Fleet and Freight Management. The Center subshystems class is one of four general subsystem classes defined in the National ITS Architecture.

A network for sharing and exchanging surface weather data and relevant surface transportation conditions. It provides a one-stop, Internet-based portal for all surface transportation environmental observations.

The original Clean Air Act was passed in 1963, but the national air pollution control program is actually based on the 1970 revision of the law. The Clean Air Act as amended in 1990 made major changes and contains the most farreaching revisions of the 1970 law.

A document of the National Architecture that provides a thorough analysis of the communications requirements of the National ITS Architecture, and ITS in general, and includes a discussion of options for implementing various communications links. It is an important document for those involved in detailed design and integration during the systems engineering process.

One of three layers (along with the transportation and institutional layers) defined by the National ITS Architecture. The communications layer includes all of the communications equipment (e.g., wireline and wireless transmitters and receivers) and the information management and transport capabilities necessary to transfer information among entities in the transportation layer. The application data content and the transportation application requirements are generally transparent to the communications layer. The communication layer's view of ITS is that of many distributed users, some of them mobile, which require communication services.

For a specific project, the document in which the project stakeholders document their shared understanding of the system to be developed and how it will be operated and maintained.

A systematic approach required in transportation management areas (TMAs) that provides for effective management and operation, based on a cooperatively developed and implemented metropolitan-wide strategy of new and existing transportation facilities eligible for funding under title 23 U.S.C. and title 49 U.S.C. through the use of operational management strategies. Provides information on transportation system performance and finds alternative ways to alleviate congestion and enhance the mobility of people and goods, to levels that meet state and local needs.

For signalized intersections, the portion of the total delay attributed to traffic signal operation.

A document of the National Architecture that has two purposes. First, it develops a high level cost estimate of the expenditures that are associated with implementing ITS components. Second, it is a costing tool for implementers, by providing unit prices and systems costs of ITS subsystems. There is significant correlation between the Cost Analysis and the Evaluatory Design documents; the cost analysis is based largely on the assumptions made for the three deployment scenarios (urban, interurban, and rural).