Office of the Assistant Secretary for Research and Technology
ITS Joint Program Office

About ITS Standards

Glossary

Application Area

Application areas refer to components of ITS systems from the deployer's perspective. The standards which apply to each of those components can be determined from the application area matrix. For example, one application area is Dynamic Message Signs (LED-based roadway signs that can be programmed to display any message). A state DOT manager who wanted to install a set of such signs could look up the Dynamic Message Sign application area in the application area matrix. He or she would then see that standards relevant to most Dynamic Message Sign deployments include NTCIP standards 1101, 1102, 1103, 1201, 1203, 2101, 2102, 2103, 2104, 2201, 2202, 2301, and 2303. This list offers a starting point for determining which standards are of interest in this DOT manager's particular project.

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.

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

The integrated application of advanced computer, electronics, and communications technologies to increase the safety and efficiency of surface transportation is known as Intelligent Transportation Systems (ITS). ITS offers a complement or an alternative to traditional engineering methods for increasing throughput, safety, etc. It makes possible increasing throughput without paying for road-widening, attracting more transit passengers without buying more buses, or reducing fuel consumption without redesigning vehicles.

ITS Architecture

Defines an architecture of interrelated systems that work together to deliver transportation services. An ITS architecture defines how systems functionally operate and the interconnection of information exchanges that must take place between these systems to accomplish transportation services. 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."

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. 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.

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

The National ITS Architecture provides a framework for planning, defining, and integrating intelligent transportation systems. It reflects the contributions of a broad cross-section of the ITS community (transportation practitioners, systems engineers, system developers, technology specialists, consultants, etc.). The Architecture represents a national consensus on the course that ITS development should take in the United States.

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

High-level design specifications based on national and regional standards and regional ITS needs.

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.

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

Subsystems correspond to the actual equipment, both hardware and software, that physically carry out the ITS functions. They are the principal structural elements of the physical architecture (which you can view by clicking on the Physical Architecture button at http://www.iteris.com/itsarch). Subsystems provide a physical representation (though not a detailed design) of important ITS interfaces and major system components. There are 19 subsystems in the National ITS Architecture. These are grouped into four classes: Centers, Roadside, Vehicles, and Travelers. Example subsystems include the Traffic Management Subsystem, the Vehicle Subsystem, and the Roadway Subsystem. Due to this close correspondence between the physical world and the subsystems, the subsystem interfaces are prime candidates for standardization.

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.

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.

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.

Working Group

Working groups consist of professionals with domain expertise in the specific ITS component to which the standard is expected to apply. They are usually a mix of SDO staff, technical consultants, and public sector (usually state-level) transportation agency representatives. A working group is selected and convened, under the direction of the sponsoring SDO, for each standard after a proposal for its development has been accepted.

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