National ITS Architecture Glossary

Existing transportation systems, communications systems, and institutional processes.

A measure of the quality of the operation of different roadway types defined in the Highway Capacity Manual (HCM). There are six LOS grades ranging from LOS A, representing optimum operation, to LOS F, representing congested or unstable flow.

A term used when denoting a progression through a series or sequence of differing stages of development.

The part of the National ITS Architecture that defines what has to be done to support the ITS user services. It defines the processes that perform ITS functions and the information or data flows that are shared between these processes. The logical architecture was developed using Structured Analysis techniques and consists of data flow diagrams, process specifications, and data dictionary entries. The logical architecture has also been called an "Essential Model" because it is not technology specific, nor does it dictate a particular implementation. This implementation independence makes the logical architecture accommodating to innovation, scalable from small scale implementations to large regional systems, and supportive of widely varied system designs.

A document of the National Architecture that contains three volumes: Description (Volume 1), Process Specifications (Volume 2), and Data Dictionary (Volume 3). These documents present a functional view of the ITS user services, contain diagrams that show processes and data flows among them, and define data elements, respectively.

Also referred to as the "Transportation Plan", a document resulting from regional or statewide collaboration and consensus on a region’s or state’s transportation system, and serving as the defining vision for the region’s or state’s transportation systems and services. In metropolitan areas, this is the official multimodal transportation plan addressing no less than a 20-year planning horizon that is developed, adopted, and updated by the MPO through the metropolitan transportation planning process.