Terminators define the boundary of an architecture. ARC-IT terminators represent the people, systems, and general environment that interface to ITS. The interfaces between terminators and the subsystems and processes within ARC-IT are defined, but no functional requirements are allocated to terminators. The functional and physical view of ARC-IT both contain the same set of terminators.

Theory of Operations

A legacy document of the National Architecture that provides a detailed description of how the National ITS Architecture supports the services described by the Service Packages. Transaction set diagrams and accompanying narrative are used to provide the detailed description. These transaction set diagrams provide sequential dependencies among the information flows in each Service Package. It is a technical document, intended for engineers, operators, and others involved in the development of regional ITS architectures or project ITS architectures.


The maximum number of people or vehicles that reasonably can be expected to traverse a point or a uniform transportation facility section during a given time period under prevailing conditions.


A measurable period during which an action, process or condition occurs.

Time synchronization

Calibration adjustment of date, hour, minutes and seconds for keeping the same time within a system.


Current hours, minutes and seconds within a day.


A cornerstone of ARC-IT is the traceability between its components (as shown in the diagram below). Microsoft Access databases are used to maintain these connections. The hyperlinked ARC-IT website relies on this traceability to build the links that allows navigation between service packages, physical, and communications views.

Traffic Management

This area addresses the management of the movement of all types of vehicles, travelers and pedestrians throughout the transportation network. It deals with information collection, dissemination, and processing for the surface transportation system. It covers both automated monitoring and control activities as well as decision-making processes (both automated and manual) that address real-time incidents and other disturbances on the transportation network, as well as managing travel demand as needed to maintain overall mobility.


A passage from one state, stage, subject, or place to another.

Transportation Alternative Study

A type of corridor study that identifies facility-specific transportation issues and opportunities within the corridor for enhancing the movement of people and goods, improvements in emergency management and response, enhancing homeland security, and ensuring opportunities for economic development. It also discusses potential options for implementation. The study is one of many that contribute to the concept and evaluation stages of the Corridor Planning and Screening Process.

Transportation Corridor

Any land area designated by the state, a county or a municipality which is between two geographic points and which area is used or is suitable for the movement of people and goods by one or more modes of transportation, including areas necessary for management of access and securing applicable approvals and permits.

Transportation Demand Management (TDM)

Programs designed to reduce demand for transportation through various means, such as the use of public transit and of alternative work hours.

Transportation Disadvantaged (TD)

Those persons who, because of disability, income status or age, are unable to transport themselves or to purchase transportation services.

Transportation Equity Act for the 21st Century (TEA-21)

Legislated in 1998, TEA-21 authorized approximately $217 billion in federal funding for transportation investment for FYs 1998- 2003. Used for highway, transit, and other surface transportation programs. Superseded in 2005 by the Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (SAFETEA-LU) legislation.

Transportation Improvement Program (TIP)

A prioritized listing/program of transportation projects covering a period of four years that is developed by an MPO as part of the metropolitan transportation planning process, consistent with the metropolitan transportation plan (MTP), and required for projects to be eligible for funding under title 23 U.S.C. and title 49 U.S.C. Chapter 53.

Transportation Management Area (TMA)

An urbanized area with a population of 200,000 or more, as defined by the U.S. Bureau of the Census and designated by the Secretary of Transportation, or any additional area where TMA designation is requested by the Governor and the MPO and designated by the U.S. Secretary of Transportation.

Transportation Network Company (TNC)

A company that uses an online-enabled platform to connect passengers with drivers using their personal, non-commercial, vehicles, e.g.: Lyft, Uber X, Sidecar, Wingz, Summon, Taxify, Haxi, Didi Kuaidi, and Arcade City.

Transportation Plan

See Long-Range Transportation Plan.

Transportation Planning Process

The process of examining travel and transportation issues and needs in an area. It includes a demographic analysis of the community in question, an examination of travel patterns and trends as well as an analysis of alternatives to meet projected future demands and for providing a transportation system that meets the community's goals and objectives. Transportation planning is a cooperative process designed to foster involvement by all users of the system. Transportation planning process is required to be organized and directed for urbanized areas by a metropolitan planning organization (MPO) and for the state by the State Department of Transportation (DOT).

Travel Time Buffer Index

A measure of the amount of extra time (buffer) that travelers need to add to their average travel time to account for non-recurring delay. The buffer is the time between the average travel time and nearworst case travel time (95th percentile). The buffer index is stated as a percentage of the average travel time and is calculated as: Buffer Index (%) = (95th percentile travel time (in minutes) - average travel time (in minutes)) / average travel time (in minutes).

Travel Time Index

The ratio of the average travel time during the peak period, using congested speeds, to the off-peak period travel time, using posted or free-flow speeds.

Travel Time Reliability

Conceptually, the ability to reach a destination on time.
1) The percent of trips that succeed in accordance with a predetermined performance standard for time or speed; and/or
2) the variability of travel times that occur on a facility or a trip over a period of time - frequently used performance measures of variability are median travel time index (TTI50), planning time index (TTI95), and buffer index.

Travel Time Savings

Reduction in total travel time for a set of future travelers once a proposed improvement is completed. This is one of the most important benefit categories projected by BCA. Managed Lanes projects and other major highway projects typically achieve most of their monetized benefits from Travel Time Savings. The preferred way to estimate future Travel Time Savings is through a travel demand model, which systematically projects a comprehensive set of future trips in the area of a major capacity improvement.


The portion of the roadway for the movement of vehicles, exclusive of shoulders.

Traveler Information

This area addresses the provision of both static and dynamic information about the transportation network to users both prior to and during their trips. It includes information about multi modal options and transfers and the status of other transportation modes for use by the users. Providing static and dynamic signage information directly to drivers through in-vehicle devices is also covered by this area.


The traversal of an entire travel pathway by a vehicle from the point of origin to a destination.


See Information Flow Triple.

Triple Solution

A solution applied to a particular information flow triple, indicating one way in which that triple might be implemented.

Turbo Architecture

Now called RAD-IT. An automated software tool used to input and manage system inventory, service packages, architecture flows and interconnects of a regional ITS architecture and/or multiple project ITS architectures.


Type, defined by the dictionary as descriptive of a particular kind, class, or group; is used in ARC-IT in 2 ways. One way 'Type' is used is to distinguish Physical Objects between System type objects, Human objects, and Other System objects. Another way 'Type' is used is to categorize Service Packages. From the Service Packages page, click "Type Sort" and see that Types of Service Packages include Convenience, Environmental, Informational, Management, Mobility, Regulatory, Safety, and Support.