Architecture - 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.”

Architecture Flow - Information that is exchanged between subsystems and terminators in the physical architecture view of the National ITS Architecture. Architecture flows are the primary tool that is used to define the Regional ITS Architecture interfaces. These 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.

Center Subsystems- 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. One of four general subsystem classes defined in the National ITS Architecture.

Communications layers or levels- As defined within the NTCIP project, these refer to five layers of technology upon which ITS systems are built. The underlying layer is the physical connection layer; intermediate layers include subnetwork type, transport protocol, and communication application choice; and the highest layer is the contents of the message that is sent. Different types of standards apply to different layers. The National ITS Architecture is based upon this stack of layers, but mostly applies to the uppermost two layers (application level and information level).

Data flows- Data flows are unaggregated types of communication which flow between subsystems within the National ITS Architecture. They are aggregated into architecture flows, which are the subject of standardization efforts.

Dedicated Short Range Communications- 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.

Deployment/deployer - Deployment is used to describe the process of implementing an standard in a real-world project. "Deployer" refers to the organization (or particular staff member) that manages the implementation.

Development status- The term "development status" refers to formal classification of the extent to which a standard in development has been reviewed and revised. Although precise criteria for promotion from one development status to the next vary slightly from SDO to SDO, the consensus-based standards development process means that the standard is continuously examined and improved before it is deemed ready to be published.

Element - This is the basic building block of Regional ITS Architectures and Project ITS Architectures. It is the name used by stakeholders to describe a system or piece of a system.

Equipment Package - Equipment packages are the building blocks 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.

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Field to Vehicle Communications- A wireless communications channel used for broadcast and interactive 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 as well as Vehicle Infrastructure Integration (VII) applications. This communication channel is supported by technologies such as 5.9 GHz Band Wireless Access in Vehicular Environments (WAVE) / Dedicated Short Range Communications (DSRC), Wi-Fi, WiMAX, and wireless mesh networks.

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

Fixed-Point to Fixed-Point Communications- 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 to 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.

Functional Requirement- 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.
Information Flow- Information that is exchanged between subsystems and terminators in the physical architecture view of the National ITS Architecture. These information flows are normally identical to the architecture flows in the National ITS Architecture. The terms "information flow" and "architecture flow" are used interchangeably.

Interface Classes- In order for a subsystem to communicate with other subsystems, one or more of the telecommunication connections ("sausages") would be used to make a link between the subsystems. Subsystem to subsystem communications are categorized by the communicating subsystem category, or interface classes. For example, the communication between a "center" subsystem and another "center" subsystem (such as a traffic management center communication with a transit management center) belongs to the center-to-center (C2C) interface class. Other communications interface classes include center-to-field (C2F), center-to-vehicle, center-to-traveler, roadside-to-vehicle, and roadside-to-roadside.

Examples of ITS applications that belong to different interface classes can be found under the application area section of the website. Applications of the same interface class will have similar requirements, specifications, and standards. For example, by looking at the physical architecture diagram, one can conclude that all C2C ITS systems require a wireline connection be in place. Indeed, all C2C applications share a common set of 11 communications protocol standards. Similarly, all C2F applications share a common set of 12 communication protocol standards. The actual data that flow on these communication links are the data flows depicted in the logical architecture. To learn more about communication interfaces, consult the National ITS Architecture Executive Summary Document.

Interoperability- ITS America's Interoperability Subcommittee adopted the following, in accord with ISO TC 204, as the definition of interoperability:"Interoperability is the ability of systems to provide services and to accept services from other systems and to use the services so exchanged to enable them to operated effectively together."In examining systems for interoperability, it is useful to distinguish two degrees of interoperability, "pair-wise" and "end-to-end" interoperability. Pair-wise interoperability involves verifying that two systems are able to exchange data and that the data has the same meaning to each system and leads to the expected functionality. "End-to-end" interoperability involves verifying that the flow and use of data are consistent from initial input to final outcome.

ITS Project - Any project that in whole or in part funds the acquisition of technologies or systems of technologies that provide or significantly contribute to the provision of one or more ITS user services.

Logical Architecture- The logical architecture view of the National ITS Architecture 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.

Market Package - The market packages provide an accessible, service-oriented perspective to the National ITS Architecture. They are tailored to fit, separately or in combination, real world transportation problems and needs. Market packages collect together one or more equipment packages that must work together to deliver a given transportation service and the architecture flows that connect them and other important external systems. In other words, they identify the pieces of the physical architecture that are required to implement a particular transportation service.

National ITS Architecture- A common, established framework for developing integrated transportation systems. The National ITS Architecture is comprised of the logical architecture and the physical architecture, which satisfy a defined set of user service requirements. The National ITS Architecture is maintained by the United States Department of Transportation (USDOT).

Physical Architecture- The physical architecture is the part of the National ITS Architecture that provides agencies with a physical representation (though not a detailed design) of the important ITS interfaces and major system components. It provides a high-level structure around the processes and data flows defined in the logical architecture. The principal elements in the physical architecture are the subsystems and architecture flows that connect these subsystems and terminators into an overall structure. The physical architecture takes the processes identified in the logical architecture and assigns them to subsystems. In addition, the data flows (also from the logical architecture) are grouped together into architecture flows. These architecture flows and their communication requirements define the interfaces required between subsystems, which form the basis for much of the ongoing standards work in the ITS program.

Project ITS Architecture- A framework that identifies the institutional agreement and technical integration necessary to interface a major ITS project with other ITS projects and systems.

Region- The geographical area that identifies the boundaries of the Regional ITS Architecture and is defined by and based on the needs of the participating agencies and other stakeholders. In metropolitan areas, a region should be no less than the boundaries of the metropolitan planning area.

Regional ITS Architecture- A specific, tailored framework for ensuring institutional agreement and technical integration for the implementation of ITS projects or groups of projects in a particular region. It functionally defines what pieces of the system are linked to others and what information is exchanged between them.

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Stakeholders- A widely used term that notates a public agency, private organization or the traveling public with a vested interest, or a “stake” in one or more transportation elements within a Regional ITS Architecture.

Standards- Standards specify how to do things consistently. They may specify how things should work, or they may describe certain physical attributes. Some everyday examples where standards are important are the keyboard you are typing on (imagine if every keyboard had different key positions) and the outlet your computer is plugged into (imagine if electrical outlets and voltages were all different). These are just a few things that use standards to help make our lives less complicated. Generally, standards are used to:

• Speed acceptance and deployment of products and services
• Enable compatibility, interchangeability, and/or interoperability
• Contain costs
• Minimize confusion
• Assure quality

Standards development organization- A standards development organization (SDO) is an organization, usually a private non-profit professional or industry organization, which manages the development of open, non-proprietary standards. Each SDO has its own strict protocol which governs the process by which drafts are created and revised with maximum input from experts in the field, so that the final product is robust, represents the best practices in the industry, and is acceptable to different types of stakeholders. In the U.S., SDOs are often accredited by the American National Standards Institute (ANSI).

Standards development process- Refers to the consensus-based protocol by which standards development organization develop open, non-proprietary standards. This process consists of convening a working group, consisting of professionals with domain expertise in the specific ITS component to which the standard is expected to apply. Their duty is to shepherd the standard draft through a series of development statuses. Promotion to each successive development status means that the draft has been reviewed by an ever-widening group of stakeholders. Thus, the standard is continuously examined and improved before it is deemed ready to be published. Revised versions may be released after this.

Subsystem- The principle structural element of the physical architecture view of the National ITS Architecture. Subsystems are individual pieces of the Intelligent Transportation System defined by the National ITS Architecture. Subsystems are grouped into four classes: Centers, Field, Vehicles, and Travelers. Example subsystems are the Traffic Management Subsystem, the Vehicle Subsystem, and the Roadway Subsystem. These correspond to the physical world: respectively traffic operations centers, automobiles, and roadside signal controllers. Due to this close correspondence between the physical world and the subsystems, the subsystem interfaces are prime candidates for standardization.

System- A collection of hardware, software, data, processes, and people that work together to achieve a common goal. Note the scope of a “system” depends on one’s viewpoint. To a sign manufacturer, a dynamic message sign is a “system.” To a state DOT, the same sign is only a component of a larger Freeway Management “System.” In a Regional ITS Architecture, a Freeway Management System is a part of the overall surface transportation “system” for the region.

Systems Engineering- A structured process for arriving at a final design of a system. The final design is selected from a number of alternatives that would accomplish the same objectives and considers the total life-cycle of the project including not only the technical merits of potential solutions but also the costs and relative value of alternatives.
System Inventory- The collection of all ITS-related elements in a Regional ITS Architecture.

Terminator- 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 views of the National ITS Architecture both have exactly the same set of terminators. The only difference is that logical architecture processes communicate with terminators using data flows, while physical architecture subsystems use architecture flows.

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

Turbo Architecture- An automated software tool used to input and manage system inventory, market packages, architecture flows and interconnects with regard to a Regional ITS Architecture and/or multiple Project ITS Architectures.

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User Services- User services document what ITS should do from the user’s perspective. A broad range of users are considered, including the traveling public as well as many different types of system operators. User services, including the corresponding user service requirements, form the basis for the National ITS Architecture development effort. The initial user services were jointly defined by USDOT and ITS America with significant stakeholder input and documented in the National Program Plan. The concept of user services allows system or project definition to begin by establishing the high level services that will be provided to address identified problems and needs. New or updated user services have been and will continue to be satisfied by the National ITS Architecture over time.

USDOT ITS JPO- The U.S. Department of Transportation's ITS Joint Program Office was created in 1994 to streamline ITS development and deployment initiatives beginning in various DOT agencies. In recognition of the interdisciplinary nature of ITS, the JPO was established to: (1) provide strategic leadership for ITS research, development, testing, and deployment, (2) guide policy coordination, and (3) ensure resource accountability. Responsibility for the actual implementation of ITS activities rests with individual program and modal administrations. These include the Federal Highway Administration (FHWA), Federal Transit Administration (FTA), the National Highway Traffic Safety Administration (NHTSA), the Federal Railroad Administration (FRA), the Federal Motor Carrier Safety Administration (FMCSA), and the Maritime Administration (MARAD).

USDOT ITS Standards Program- The USDOT's ITS Standards Program is a consensus-building effort to promote the widespread deployment of interoperable ITS systems by supporting the participation of stakeholders and accelerating the development and deployment of ITS standards. The major program elements are Standards Development, Standards Testing, Outreach and Education, Technical Assistance, and Policy Support.

Vehicle Subsystems- Covers ITS related elements on vehicle platforms. Vehicle subsystems include general driver information and safety systems applicable to all vehicle types. Four fleet vehicle subsystems (Transit, Emergency, Commercial and Maintenance and Construction Vehicles) add ITS capabilities unique to these special vehicle types. One of four general subsystem classes defined in the National ITS Architecture.

Vehicle to Vehicle Communications- Dedicated wireless system handling high data rate, low probability of error, line of sight communications between vehicles. Advanced vehicle services may use this link in the future to support advanced collision avoidance implementations, road condition information sharing, and active coordination to advanced control systems. One of the types of architecture interconnects defined in the National ITS Architecture.

Wide Area Wireless Communications- A communications link that provides communications via a wireless device between a user and an infrastructure-based system. Both broadcast (one-way) and interactive (two-way) communications services are grouped into wide-area wireless communications in the National ITS Architecture. These links support a range of services in the National ITS Architecture including real-time traveler information and various forms of fleet communications. One of the types of architecture interconnects defined in the National ITS Architecture.

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