A framework within which a system can be built. Requirements dictate what functionality the architecture must satisfy. An architecture functionally defines what the pieces of the system are and the information that is exchanged between them. An architecture is functionally oriented and not technology-specific which allows the architecture to remain effective over time. It defines "what must be done," not "how it will be done."

Information that is exchanged between subsystems and terminators in the physical architecture of the National ITS Architecture. Architecture flows are the primary tool that is used to define interfaces in regional ITS architectures and project ITS architectures. Architecture flows and their communication requirements define the interfaces which form the basis for much of the ongoing standards work in the national ITS program. The terms "information flow" and "architecture flow" are used interchangeably.

Communications paths that carry information between subsystems and terminators in the physical architecture of the National ITS Architecture. Several different types of interconnects are defined in the National ITS Architecture to reflect the range of interface requirements in ITS. The majority of the interconnects are various types of communications links that are defined in the communications layer. Four different types of communications links are defined: Fixed Point - Fixed Point Communications, Wide Area Wireless (Mobile) Communications, Field - Vehicle Communications, and Vehicle - Vehicle Communications. In addition to these types, several specialized interconnects are also defined to reflect other interface requirements. These include human interface (e.g., what the system user sees and hears) and physical/environmental (e.g., what the ITS sensors sense).

A term used in transit operations to describe a vehicle work assignment, i.e. a sequence of trips made by a single bus. Blocks can be divided between different operators.

A type of software that allows viewing of and navigation through HTML pages.

See travel time buffer index.

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).

Every data flow included in the logical architecture of the National ITS Architecture is defined in a data dictionary entry. Each data dictionary entry contains a textual description of the data flow and identifies any lower level data elements that make up the data flow.

Representations of data flowing between processes or between a process and a terminator in the logical architecture of the National ITS Architecture. A data flow is shown as an arrow on a data flow diagram and is defined in a data dictionary entry in the logical architecture. Data flows are aggregated together to form high-level architecture flows in the physical architecture of the National ITS Architecture.

The diagrams in the logical architecture of the National ITS Architecture that show the functions that are required for ITS and the information that moves between these functions. Only four different symbols are used on the diagrams. Circles represent the processes or functions that do the work. Arrows represent the data flows that show how data moves through the system. Parallel lines represent data stores that represent "data at rest" in the system. Finally, rectangles represent the terminators that define the architecture boundary. A hierarchy of these diagrams depict the ITS functionality and data flow requirements in successively greater detail until "primitive" processes are defined.

A data store represents a reservoir in which data can be held for an indefinite period. Data stores are shown on the data flow diagrams where data repositories are required to support data aggregation or archival services.

An ITS system or piece of a system named as the name used by stakeholders. Elements are the basic building blocks of regional ITS architectures and project ITS architectures.

Enhanced Metafile. A graphics file format, originated by Microsoft Corporation, that has many advantages over the older Windows metafiles (WMF). Images in EMF format can be resized without distortion and loss of detail. Available for download for selected diagrams (e.g., subsystem and terminator diagrams). Many diagrams displayed on the National ITS Architecture CD-ROM and web site are actually in GIF format.

The building blocks of the subsystems of the physical architecture subsystems. Equipment packages group similar processes of a particular subsystem together into an “implementable” package. The grouping also takes into account the user services and the need to accommodate various levels of functionality. The equipment packages were used as a basis for estimating deployment costs (as part of the evaluation that was performed). Since equipment packages are both the most detailed elements of the physical architecture of the National ITS Architecture and tied to specific service packages, they provide the common link between the interface-oriented architecture definition and the deployment-oriented service packages.

A document of the National Architecture that contains a concise summary of the various evaluations that were performed in five other National ITS Architecture documents: Evaluatory Design, Communications Document, Cost Analysis, Performance and Benefits Study, and Risk Analysis.

A document of the National Architecture that supports evaluation of the National ITS Architecture's performance, benefits, and costs for three conceptual scenarios at various points in time. The scenarios consist of "typical" deployment environments: urban, inter-urban, and rural. The entire document will assist you in developing an evaluation methodology for the architecture that you have developed for your particular region or project.

A document of the National Architecture that provides an overview of the most important aspects of the National ITS Architecture including the logical architecture, physical architecture and the implementation strategy.

An agency of the United States Department of Transportation. FHWA administers the Federal-aid Highway Program, which provides financial assistance to States to construct and improve highways, urban and rural roads, and bridges. FHWA also administers the Federal Lands Highway Program, which provides access to and within national forests, national parks, Indian Tribal lands, and other public lands. FHWA is headquartered in Washington, DC, with field offices across the country, including one in or near each State capital.

An agency of the United States Department of Transportation. FTA is the principal source of Federal financial assistance to America's communities for the planning, development, and improvement of public or mass transportation systems. FTA provides leadership, technical assistance, and financial resources for safe, technologically advanced public transportation that enhances mobility and accessibility, improves the nation's communities and natural environment, and strengthens the national economy. FTA is headquartered in Washington, DC, with regional offices in Atlanta, Boston, Chicago, Dallas, Denver, Kansas City, New York, Philadelphia, San Francisco, and Seattle.

A wireless communications channel used for close-proximity communications between vehicles and the immediate infrastructure. It supports location-specific communications for ITS capabilities such as toll collection, transit vehicle management, driver information, and automated commercial vehicle operations. One of the types of architecture interconnects defined in the National ITS Architecture.

Intelligent infrastructure distributed along the transportation network which performs surveillance, information provision, and plan execution control functions and whose operation is governed by center subsystems. Field subsystems also directly interface to vehicle subsystems. The Field subsystems class is one of the four general subsystem classes defined in the National ITS Architecture.

A communication link serving stationary entities. It may be implemented using a variety of public or private communication networks and technologies. It can include, but is not limited to, twisted pair, coaxial cable, fiber optic, microwave relay networks, spread spectrum, etc. In Fixed Point - Fixed Point (FP2FP) communication the important issue is that it serves stationary entities. Both dedicated and shared communication resources may be used. One of the types of architecture interconnects defined in the National ITS Architecture.

A statement that specifies WHAT a system must do. The statement should use formal “shall” language and specify a function in terms that the stakeholders, particularly the system implementers, will understand. In the National ITS Architecture, functional requirements have been defined for each Equipment Package that focus on the high-level requirements that support regional integration.

Graphic Interchange Format. A widely used graphics file format, developed by CompuServe. Many images found on the National ITS Architecture CD-ROM and web site are in GIF format and can be typically be copied by right-clicking on them with your mouse. Unlike WMF files, GIF files are not well suited for resizing or other modifications.

In long range transportation plans, generalized statements which broadly relate the physical environment to values.

Vehicles carrying two or more people. The number that constitutes an HOV for the purposes of HOV highway lanes may be designated differently by different transportation agencies.

HyperText Markup Language. A language for marking up documents with a set of tags that designate the design and display intention of the author and how sections or documents are linked together. These documents are displayed as pages with text and graphics that can be viewed through the use of a browser.

A document of the National Architecture that presents a scheme for implementing ITS services in a phased approach. This is part of an overall strategy that includes recommendations for future research and development, operational tests, standards activities, and training. The Implementation Strategy analysis and guidance is all based on service packages. It identifies the service packages that provide certain ITS services and recommends a phased deployment of those service packages to provide the most needed and most feasible user services initially, and less needed/feasible user services at a later date. The Implementation Strategy considers several items and issues regarding deployment, such as legacy systems, politics, funding, service package synergy, technology requirements, and standards requirements. Much of the service package-related analysis that is contained in the Implementation Strategy has been updated and included in the new Service Packages Document. The Service Packages Document is the authoritative source for all current information on the National ITS Architecture service packages.

Information that is exchanged between subsystems and terminators in the physical architecture of the National ITS Architecture. The terms "information flow" and "architecture flow" are used interchangeably. Information flows are the primary tool that is used to define the ITS architecture interfaces. These information flows and their communication requirements define the interfaces which form the basis for much of the ongoing standards work in the national ITS program.

An integral component of the National ITS Architecture that represents the existing and emerging institutional constraints and arrangements that are the context for all ITS deployments. The transportation layer and communications layer together provide the technical framework within which interoperable systems may be implemented. The institutional layer introduces the policies, funding incentives, working arrangements, and jurisdictional structure that support the technical layers of the architecture. This institutional layer provides the basis for understanding who the stakeholders will be and the roles these implementers could take in implementing architecture-based ITS systems.

The system defined as the electronics, communications or information processing in transportation infrastructure and in vehicles used singly or integrated to improve transportation safety and mobility and enhance productivity. Intelligent transportation systems (ITS) encompass a broad range of wireless and wire line communications-based information and electronics technologies.

See architecture interconnect.

The ability to connect, and connections between, differing modes of transportation.

Legislative initiative by the U.S. Congress that restructured and authorized federal funding for transportation programs; provided for an increased role for regional planning commissions/ MPOs in funding decisions; and required comprehensive regional and statewide longterm transportation plans. Superseded by the Transportation Equity Act for the 21st Century (TEA-21) in 1998.

See system inventory.