Identity Certificate

A certificate that uses a digital signature to bind a public key with an identity - information such as the name of a person or an organization, their address, and so forth. The certificate can be used to verify that a public key belongs to an individual.

Implementation Strategy

A legacy 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 was updated and included in the newer Service Packages Document. The Service Packages Document was the authoritative source for information on the National ITS Architecture service packages.

Information Flow

The provision of information from one Physical Object to another in the physical view of ARC-IT. An information flow may include one or more other information flows (i.e., one flow is a sub-flow of another). An information flow may include message exchanges used to control the flow of information. An information flow may be unidirectional or bidirectional. Regardless, the informative description defines the information provided by the source.

Information flows appear on service package diagrams as solid lines with an arrow at one or both ends that indicate the direction information is flowing, as shown below.

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.

Note: The terms "information flow" and "architecture flow" are used interchangeably.

Information Flow Characteristics

Quantitative or qualitative enumeration of particular aspects of an information flow. Characteristics are defined to help address concerns related to applicable communications technologies, necessary cybersecurity support, use of standards and consistency between deployments. As of V9.1, ARC-IT defines nine characteristics for each information flow triple:

Latency: describes a requirement restricting the maximum acceptable amount of time for the information to be received relative to when the information was generated; e.g., 'Ultralow' is <200ms, while 'Low' <2s.

Cardinality: describes the typical distribution mechanism; e.g. 'Broadcast' means the information is sent once and all instances of the receiver physical object receive the data simultaneously, whereas 'Unicast' means the information is sent individually to each recipient.

Time Context: the relative time range over which the data contained in the information flow is relevant; e.g., 'Now' suggests the data is only relevant for a few seconds.

Spatial Context: the relative geographic range over which the data contained in the information flow is relevant; e.g. 'Local' suggests that data is relevant to typical line-of-sight, while 'Adjacent' is relevant to an intersection or smaller area.

Acknowledgement: Identifies whether the information flow requires the receiver to acknowledge receipt.

Encryption: Identifies whether information sent in this flow should be obfuscated, typically using some kind of application-layer encryption technology.

Authentication: identifies whether the information contained information flow should have integrity protection, and authentication of the information sender (nearly always 'yes').

Initiator: identifies whether the information source or information receiver is typically the initiator of the information flow.

Interoperability: the deployment scope to which implementations of this triple should be common; e.g., 'National', suggests that the flow should be implemented using the same solution throughout the country.

See also the Physical Viewpoint specification for a guide on how these characteristics reflected in service package diagrams.

Information Flow Triple

The combination of source physical object, information flow and destination physical object. See also Triple; see also Information Transfer.

Information Flow Triple Relationship

Dependencies and interactions between information flow triples. These relationships come in three types: "Interactive" relationship between triples means that one triple may prompt a response by the physical object for the other triple. "Request-response" relationship means that a request message on one triple will prompt a response message by the physical object for the other triple. A "depends-on" relationship means that one triple cannot be implemented without the other triple. Typically, a flow output by a physical object 'depends-on' a flow received by the physical object, as illustrated below, where the 'environmental situation data' flow sent by the Connected Vehicle Roadside Equipment depends on the 'vehicle environmental data' flow it receives.

Information Transfer

See Information Flow Triple.


Having different forms of transportation with different infrastructure, information systems and payment structures combined to form a single, unified transportation system.


1) To maintain a system that is secure, complete and conforming to an acceptable conduct without being vulnerable and corruptible.

2) A cryptographic service that provides assurance that any changes to a protocol data unit (PDU) made after it is validly created will be detected.

Intelligent Transportation System (ITS)

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.

Interface Standard

Standard defining necessary capabilities and requirements to be met by interfacing systems to achieve data exchange.


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

Intermodal Center

An existing or planned transportation facility providing an interface between more than one mode of transportation [at least one of which must provide interstate or interregional service to be designated as Strategic Intermodal System (SIS) or Emerging SIS]. An example of an intermodal center is the Miami Intermodal Center (MIC), which provides connections between Amtrak, Tri-Rail and the local transit system.

Intermodal Surface Transportation Efficiency Act of 1991 (ISTEA)

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.


An interconnected system of networks that connects computers around the world via the Transport Control Protocol / Internet Protocol (TCP/IP).


The ability of two or more systems or components to exchange information and to use the information that has been exchanged.


Relating to the connection between any two or more regions.


In the context of this standard an intersection is a nexus where two or more approaches (links) meet and vehicles and other type users may travel between the connecting links. Typically this is a signalized intersection when considered by this architecture, and as such the modes of allowed movement are reflected in the signal phases, the geometry of the intersection, and the local regulatory environment. The messages convey some of this intersection information to the traveling public. Specifically, the MAP message conveys the relevant road geometry, while the SPaT message conveys the current allowed movements to control movement in the intersection.


Relating to the connections that have both ends within a single region.


See system inventory.

Inventory Element

See element.

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.

ITS Knowledge Resources

Access point for four Web-based resources that provide ready access to information supporting informed decision making regarding deployment and operations of ITS to improve transportation system performance. The four knowledge resources are the ITS Benefits Database, ITS Costs Database, ITS Deployment Statistics Database, and the ITS Lessons Learned Knowledge Resource. A fifth Web site, the ITS Applications Overview, provides access to information from each of the knowledge resources using an organization structure. The ITS Knowledge Resource Portal is available at

ITS Physical Objects

Physical Objects that provide core capabilities and interfaces that may be included in any ITS system or device. The ITS class is one of six general Physical Object classes defined in ARC-IT. The ITS class objects are typically shown as grey boxes on service package drawings.

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.

ITS Standards

Standards developed specifically to meet ITS needs. See Standard.