National ITS Architecture Glossary

Terminators define the boundary of an architecture. The National ITS Architecture terminators represent the people, systems, and general environment that interface to ITS. The interfaces between terminators and the subsystems and processes within the National ITS Architecture are defined, but no functional requirements are allocated to terminators. The logical architecture and physical architecture of the National ITS Architecture both contain the same set of terminators.

A document of the National Architecture that provides a detailed description of how the National ITS Architecture supports the services described by the Service Packages. Transaction set diagrams and accompanying narrative are used to provide the detailed description. These transaction set diagrams provide sequential dependencies among the information flows in each Service Package. It is a technical document, intended for engineers, operators, and others involved in the development of regional ITS architectures or project ITS architectures.

A cornerstone of the National ITS Architecture is the traceability between its components (as shown in the diagram below). Microsoft Access databases are used to maintain these connections. The hyperlinked National ITS Architecture relies on this traceability to build the links that allows navigation between user services, logical architecture, and physical architecture.

Programs designed to reduce demand for transportation through various means, such as the use of public transit and of alternative work hours.

Legislated in 1998, TEA-21 authorized approximately $217 billion in federal funding for transportation investment for FYs 1998- 2003. Used for highway, transit, and other surface transportation programs. Superseded in 2005 by the Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (SAFETEA-LU) legislation.

A prioritized listing/program of transportation projects covering a period of four years that is developed by an MPO as part of the metropolitan transportation planning process, consistent with the metropolitan transportation plan (MTP), and required for projects to be eligible for funding under title 23 U.S.C. and title 49 U.S.C. Chapter 53.

One of three layers (along with the communications layer and the institutional layer) defined by the physical architecture. The transportation layer shows the relationships among the transportation related elements. It is composed of subsystems for travelers, vehicles, transportation management centers, and field devices, as well as external system interfaces (terminators) at the boundaries.

An urbanized area with a population of 200,000 or more, as defined by the U.S. Bureau of the Census and designated by the Secretary of Transportation, or any additional area where TMA designation is requested by the Governor and the MPO and designated by the U.S. Secretary of Transportation.

See Long-Range Transportation Plan.

The process of examining travel and transportation issues and needs in an area. It includes a demographic analysis of the community in question, an examination of travel patterns and trends as well as an analysis of alternatives to meet projected future demands and for providing a transportation system that meets the community’s goals and objectives. Transportation planning is a cooperative process designed to foster involvement by all users of the system. Transportation planning process is required to be organized and directed for urbanized areas by a metropolitan planning organization (MPO) and for the state by the State Department of Transportation (DOT).

A measure of the amount of extra time (buffer) that travelers need to add to their average travel time to account for non-recurring delay. The buffer is the time between the average travel time and nearworst case travel time (95th percentile). The buffer index is stated as a percentage of the average travel time and is calculated as: Buffer Index (%) = (95th percentile travel time (in minutes) - average travel time (in minutes)) / average travel time (in minutes).

The ratio of the average travel time during the peak period, using congested speeds, to the off-peak period travel time, using posted or free-flow speeds.

Equipment used by travelers to access ITS services pre-trip and en-route. This includes equipment that are owned and operated by the traveler as well as equipment that are owned by transportation and information providers. The Traveler subsystems class is one of four general subsystem classes defined in the National ITS Architecture.

An automated software tool used to input and manage system inventory, service packages, architecture flows and interconnects of a regional ITS architecture and/or multiple project ITS architectures.