Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (SAFETEA-LU)

Legislation passed in 2005 that authorized the federal surface transportation programs for highways, highway safety, and transit.

Safety Analysis

A comprehensive assessment of safety outcomes with and without a specific project under consideration, including a general analysis of historical crash data on the facility under consideration, a detailed review of fatal crashes and their causes, field inspections at the locations where a high concentration of crashes occurred, recommendations for potential corrective countermeasures, and evaluation of the proposed countermeasures.

Safety Management System

A systematic process that has the goal of reducing the number and severity of traffic crashes by ensuring that all opportunities to improve highway safety are identified, considered, implemented as appropriate and evaluated in all phases of highway planning, design, construction, maintenance and operation; and by providing information for selecting and implementing effective highway safety strategies and projects.

Safety Program

Projects designed to improve vehicle and pedestrian safety on the city, county and state highway systems. The program is divided into three subprograms rail/highway crossings, highway safety and traffic safety grants.


To select a subset of a larger group, usually in a regular pattern (e.g., 1 of every 10).


The capable of being easily grown, expanded or upgraded upon demand without requiring a redesign.

Scalable Vector Graphics

Scalable Vector Graphics (SVG) is a language for describing two-dimensional graphics and graphical applications that is backed by the World Wide Web Consortium. Graphics described in SVG file format can be scaled without losing graphic quality. SVG files can be compressed to accommodate faster downloads of the graphic. ARC-IT uses compressed SVG format to view the physical and enterprise diagrams on the Service Packages pages. The first time you open one of these diagrams you may be prompted to download an SVG Viewer as an add-on to your existing Web Browser.


A step-by-step description of a series of events that may occur concurrently or sequentially. One of the components of a Concept of Operations (ConOps) document.

Secure Storage

Encrypted or protected data that requires a user or a process to authenticate itself before accessing to the data. Secure storage persists when the power is turned off.

Secure Transmission

To protect the transfer of confidential or sensitive data usually by encryption, Secure Sockets Layer (SSL), Hypertext Transfer Protocol Secure (HTTPS) are common examples of secure communications.


Referring to storage, which consists of both logical and physical safeguards.

Securing ITS

The protection of ITS itself is comprised of security services that protect ITS systems and the communications between them. See the Security Document for more information.

Security Objective

Providing security for the surface transportation system has a set of desired outcomes (or objectives). How well a security system performs can be measured by the extent to which it meets the desired objectives.

Security Services

Security services are typical security mechanisms or countermeasures that provide for different aspects of security.

Security Threat

Security threats are events or circumstances that adversely impact a surface transportation system or communication between systems.

Self-Driving Vehicle

See automated vehicle.

Service Channel

Any channel that is not the control channel, intended for management frames and higher layer information exchanges. There may be more than one service channel defined in a given spectrum.

Service Package

The service packages, formerly known as market packages, provide an accessible, service-oriented perspective to ARC-IT. They were also known as "applications" in CVRIA. They are tailored to fit, separately or in combination, real world transportation problems and needs. Service packages collect together one or more Functional Objects that must work together to deliver a given ITS service and the information flows that connect them and other important external systems. In other words, they identify the pieces of the physical view that are required to implement a particular ITS service. Service packages are implemented through projects (or groups of projects, aka programs) and in transportation planning, are directly related to ITS strategies used to meet regional goals and objectives.

Service Package Implementation

A subset of a service package that defines an approach for meeting the user needs of a given service package. Some service packages provide multiple ways or implementations to satisfy meeting the user needs driving the inclusion of a service package. An implementation indicates what functions and flow triples are required, and which flows and functions may enhance the service without duplicative effort or interference.

Service Specific Permissions

A field that indicates the permissions of a particular certificate holder with respect to a particular application area.

Session-oriented Connection

A connection between two networked devices that is established intermittently and to handle few requests thereafter. The connection is meant to be temporary lasting for minutes, hours, but likely not more than a day before it is closed. This is opposite of Persistent Connection.

Shared Roadway

A roadway that is open to both bicycle and motor travel.

Shared Use Path

A multi-use trail or other path, physically separated from motorized vehicular traffic by an open space or barrier, either within a highway right-of-way or within an independent right-of-way, and usable for transportation purposes; used by pedestrians, bicyclists, skaters, equestrians, and other no motorized users.

Short Range Wireless Communications

A wireless communications channel used for close-proximity communications between vehicles, mobile/personal devices, and the immediate infrastructure. It supports location-specific communications for ITS capabilities such as vehicle safety, transit vehicle management, driver information, roadway payments, and automated commercial vehicle operations. One of the types of interconnects defined in the Architecture Reference for Cooperative and Intelligent Transportation (ARC-IT).


A report including one or more status elements in the vehicle at a single point in time, along with a set of position and heading elements.


Software is a general term that describes computer programs. Terms such as software programs, applications, scripts, and instruction sets all fall under the category of computer software.


A set of standards arranged as per the ARC-IT communications model.


Signal Phase And Timing (SPaT), a message type that describes the current state of a signal system and its phases and relates this to the specific lanes (and therefore to movements and approaches) in the intersection. It is used along with the MAP message to allow describing an intersection and its current allowed movements.


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 or project ITS architecture.


A formal specification that defines and governs some function or attribute of an implementation. See interface standard, physical standard.

Standards Development Plan

A legacy document of the National Architecture that discusses the issues that are involved in the development of system interface standards. It was primarily intended as a planning document for US DOT and the Standards Development Organizations.

States or Modes

A distinct system setting in which the same user input will produce different results than it would in other settings. The System as a whole is always in one state. A state is typically commanded or placed in that state by an operator.

Statewide Transportation Improvement Program (STIP)

A statewide prioritized listing/program of transportation projects covering a period of at least four years that is consistent with the long-range statewide transportation plan (LRSTP), metropolitan transportation plans (MTPs), and transportation improvement plans (TIPs), and is required for projects to be eligible for funding under title 23 U.S.C. and title 49 U.S.C. Chapter 53.

Statewide Transportation Plan

The official statewide multimodal, long-range transportation plan addressing no less than a 20-year planning horizon that is developed, adopted and updated by the state DOT through the statewide transportation planning process.


Anomalies, actions, intermittent and other conditions used to inform the System Operator for reparation or maintenance.

Strategic Highway Network (STRAHNET)

A network of highways which are important to U.S. strategic defense policy and which provide defense access, continuity and emergency capabilities for defense purposes.


A specific activity that is designed to help achieve an objective.


'Stratum' refers to the number of levels removed from the source or reference clock. Stratum-1 time servers are time servers that are directly connected to a basic time source by a hardwire connection (e.g., RS-232). The reference clock typically synchronizes to the correct time (UTC) using GPS transmissions, CDMA technology or other time signals.


'Stratum' refers to the number of levels removed from the source or reference clock. Stratum-2 servers are time servers that are 2 steps removed from a basic time source (e.g., atomic clock). Stratum-2 time servers request time from Stratum-1 servers.


The principle structural element of the physical view of ARC-IT. Subsystems are individual pieces of the Intelligent Transportation System defined by ARC-IT. Subsystems are defined at three levels of hierarchy: ITS Objects, Classes, and Functional Subsystems. See the physical view page for an illustration of the relationships between different levels of this hierarchy. Subsystems are grouped into 5 classes: Center, Field, Personal, Support and Vehicle. There are more than 100 functional subsystems; examples include the Traffic Management Center, ITS Roadway Equipment, Personal Information Device, Cooperative ITS Credential Management System and Light Vehicle On-Board Equipment (OBE). These correspond to the physical world: respectively traffic operations centers, roadside intelligent infrastructure such as traffic signal controllers, smartphones, security credentials management systems and the telematics and communications-centric safety systems on passenger automobiles. Due to this close correspondence between the physical world and the subsystems, subsystem interfaces are prime candidates for standardization.

Subsystem Diagram

A diagram which depicts all subsystem Physical Objects in ARC-IT and the basic communication channels between these subsystems. The subsystem diagram is a top-level architecture interconnect diagram. Variations of the subsystem diagram are sometimes used to depict regional ITS architectures or project ITS architectures at a high level.

Super Flow

An information transfer where the origin and/or the destination is a general physical object, i.e., one of ITS Object, Center, Field, Support, Vehicle, or Personal.


This area addresses monitoring, maintaining, and managing of the connected vehicle system, which includes, centers, field equipment, vehicles, and traveler devices. In addition, it covers the security and privacy of the communications in the connected vehicle environment as well as fundamental services, such as location and data distribution that support the full range of ITS services.

Support Service

A provision of an interface of an object to support actions of another object. Or more simply, to provide (someone or something) with something that is needed or wanted. Support services enable the secure, managed operation of ITS Application Entities.


Meeting the needs of the present without compromising the ability to meet the needs of the future.

Sustainable Travel

This area addresses the operation of transportation system to minimize the environmental impact. It promotes a transportation system that balances accessibility, mobility, protection of human safety and environment. It covers all aspects of transportation system from optimizing traffic signals and ramp meters to managing HOV/HOT lanes, monitoring vehicle emissions and managing vehicle electric charging stations.

Symmetric Cryptographic Algorithm

A cryptographic algorithm that uses a single key. Knowledge of a symmetric encryption key allows both encryption and decryption. Knowledge of a symmetric authentication key allows generation and verification of message authentication codes.


The act or results of occurrence or operating at the same time or rate.


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 or project ITS architecture, a Freeway Management System is a part of the overall surface transportation "system" for the region.

System Element

1) A collection of interacting components organized to accomplish a specified function or set of functions within a specified environment.

2) An object and procedures constituted to achieve defined objectives of some operational role by performing specified functions. A complete system element includes all of the associated equipment, facilities, material, computer programs, firmware, technical documentation, services, and personnel required for operations and support to the degree necessary for self-sufficient use in its intended environment. An integrated set of components that accomplish a clearly distinguishable set of functions with similar or related uses.

System Elements include but are not limited to instantiations of Physical Objects, Functional Objects, and Enterprise Objects.

System Inventory

The list of all ITS-related elements in a regional ITS architecture or project ITS architecture.

System Maintenance

Actions taken to preserve the state's transportation infrastructure investment (e.g., resurfacing pavements of roadways and airport runways, repairing and replacing bridges, maintaining existing transit routes and frequencies) to eliminate deficiencies and to extend/achieve the expected life of facilities before, for example, reconstruction is needed.

System Need

A capability that is identified and supported within the System to accomplish a specific goal or solve a problem.

System of Systems

A system whose elements are themselves systems. A system of systems (SoS) brings together a group of systems to accomplish a mission that none of the systems can accomplish on their own. Most ITS service packages represent a system of systems.

System Personnel

The staff that operates and maintains the System. In addition to network managers and operations personnel, System Personnel includes the Administrators, Operators, Maintainers, Developers, Deployment teams, and Testers.

System User

System Users refers to Mobile, Field, and Center Systems - the components/elements of the overall domain that interact with each other to access system resources and share information.

Systems Engineering

Defined by International Council on Systems Engineering (INCOSE) as an interdisciplinary approach and means to enable the realization of successful systems. It focuses on defining customer needs and required functionality early in the development cycle, documenting requirements, and then proceeding with design synthesis and system validation while considering the complete problem. Systems engineering integrates all the disciplines and specialty groups into a team effort forming a structured development process that proceeds from concept to production to operation. Systems engineering considers both the business and the technical needs of all customers with the goal of providing a quality product that meets the user needs.