Parking Management

This area addresses the management of parking operations including both space management and the electronic payment for parking. This area supports communication and coordination between equipped parking facilities and regional coordination between parking facilities and traffic and transit management systems. It includes monitoring and managing parking spaces and in lots, garages, and other parking areas and facilities as well as loading/ unloading zones.


To extract individual elements from a larger message.

Pavement Condition Index

Based on a visual survey of the pavement, a numerical index of 0 to 100 to indicate the condition of the pavement on a roadway with 100 representing an excellent pavement.

Peak Hour

1) The hour in which the greatest amount of travel occurs (typically considered 5:00-6:00 p.m. on a weekday);
2) The hour in which the greatest amount of travel occurs for a mode.

Peak Period

1) A multi-hour period in which travel is greatest;
2) For the auto mode in large urbanized areas the two-hour weekday time period of 4:00-6:00 p.m. at which congestion is typically highest.

Performance and Benefits Study

A legacy document of the National Architecture that assessed the technical performance of the National ITS Architecture on a number of system-level and operational-level criteria. It was helpful in supporting the case for ITS deployment, as it provided a measure of the degree to which ITS could help achieve some regional transportation goals.

Performance Measure

Indicator of how well the transportation system is performing with regard to such measures as average speed, reliability of travel, and accident rates. Used as feedback in the decisionmaking process.

Performance-Based Planning and Programming Process

The process developed to monitor progress toward achieving goals and objectives at the agency strategic, decision-making and project delivery levels.

Persistent connection

A connection between two networked devices that remains open after the initial request is completed, to handle multiple requests thereafter. This reduces resource overhead of re-establishing connections for each message sent and received. This is opposite of Session-oriented Connection.

Personal Physical Objects

Equipment used by travelers and others using personal devices to access transportation services pre-trip and en-route. This includes equipment that are owned and operated by the traveler/person as well as equipment that are owned by agencies and used/worn by staff/personnel. The Personal class is one of six general object classes defined in the Architecture Reference for Cooperative and Intelligent Transportation (ARC-IT).

Physical Entities

See Physical Object.

Physical Object

Systems or devices that provide ITS functionality of an intelligent transportation system (ITS) and the surrounding environment. Physical Objects are defined in terms of the services they support, the processing they include, and their interfaces with other Physical Objects. They are grouped into six classes:

- Centers, which exist remote from the transportation environment and may be a traditional 'brick and mortar' facility or for software-intensive systems may be cloud-based, e.g., ' Traffic Management Center.' See 'Center Physical Objects.'
- Field, typically devices proximate to the transportation environment, e.g., 'ITS Roadway Equipment.' See 'Field Physical Objects.'
- ITS, which are objects that provide core capabilities that may be included in any other class. See 'ITS Physical Objects.'
- Personal, which includes devices used by individual travelers, e.g., 'Personal Information Device.' In older versions of the national ITS architecture, this class was called 'Travelers.' See 'Personal Physical Objects.'
- Support, which provide information and/or functionality that support ITS services but do not directly provide an ITS service'; e.g., 'Cooperative ITS Credentials Management System.'
- Vehicles, which include all wheeled conveyances but are generally focused on the ITS components inside those conveyances, e.g., 'Transit Vehicle OBE.' See 'Vehicle Physical Objects.'

Due to the close correspondence between the physical world and Physical Objects, the interfaces between them are prime candidates for standardization.

In ARC-IT, Physical Objects are defined with scope such that they are under the control of a single Enterprise Object. In all cases, a human physical object may be associated with the class of the physical object with which it interacts, e.g., 'Driver' is classed as a 'Vehicle' type.

Physical Security

Safeguards to deny access to unauthorized personnel (including attackers or even accidental intruders) from physically accessing a building, facility, resource, or stored information. This can range from simply a locked door to badge entry. with armed security guards

Physical Standard

Standard defining material attributes, environmental performance, physical security and other aspects of an implementation.

Physical View

The part of ARC-IT that provides deployers and agencies with a physical representation (though not a detailed design) of the important interfaces and major system components. It describes the connections between Physical Objects within the intelligent transportation system environment. It provides a high-level structure around the processes and data flows defined in the Functional View. The principal elements in the physical view are the Physical Objects and information flows that connect these Physical Objects into an overall structure. These information flows and their communication requirements define the interfaces required between Physical Objects, which form the basis for much of the ongoing standards work in the ITS program.

Planning Factors

As specified in the Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (SAFETEA-LU) legislation (in Section 5303 and Section 5304 of Title 49 of the United States Code), the nine areas which metropolitan planning organizations (MPOs) and states should consider when developing their transportation plans.

Planning for Operations

A joint effort between planners and operators to support improved regional transportation system management and operations that involves a variety of activities that lead to improved transportation system operations, including the consideration of management and operations strategies in the transportation planning process.

Planning Time Index

A measure of the amount of extra time that travelers need to add to free-flow (or posted speed limit) travel time in order to arrive on-time in almost all situations (i.e. 95% of the time). The planning time index takes into account both recurring and non-recurring sources of delay. The planning time index is calculated as 95th percentile travel time (in minutes) / Travel time at free flow speed or posted speed limit (in minutes).


Portable Network Graphics file. A graphics file format that has many advantages, including their compatibility across browsers and office applications. Images in PNG format can be resized without distortion and loss of detail. Available for download for selected diagrams (e.g., application diagrams). Many diagrams displayed on the ARC-IT web site are in PNG format.


A set of guidelines and constraints on the behaviors and states exhibited by the objects in the ARC-IT.


A rank order of status, activities, or tasks. Priority is particularly important when resources are limited.


The ability of an individual to seclude information about themselves, and thereby reveal information about themselves selectively. From the VII Privacy Policies Framework: the respect for individual choices about, and control over an individual's personal information.

Problem domain

A set of similar problems that occur in an environment and lend themselves to common solutions.


A function or activity identified in the Functional View of ARC-IT that is required to support the ITS requirements. The functional view presents processes in a top-down fashion beginning with general processes (e.g., "Manage Traffic") that are then decomposed into more detailed processes (e.g., "Provide Traffic Surveillance", "Monitor HOV Lane Use"). The most detailed processes (sometimes called primitives) are defined in Process Specifications (PSpecs).

Process Specification (pspec)

The textual definition of the most detailed processes identified in the functional view of ARC-IT. The process specification includes an overview, a set of functional requirements, and a complete set of inputs and outputs.

Project Architecture

A framework that identifies the institutional agreement and technical integration necessary to implement an ITS project, including integration with other ITS projects and systems.

Project Development

The process used to implement a project. Typically for traditional transportation construction project involves phases of project initiation, preliminary engineering, plan development, construction and project closeout. Also referred to as project deployment or project implementation.

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.


As in Communications Protocol - A system of rules that allow two or more entities of a communications system to transmit information via any kind of variation of a physical quantity. Communicating systems use well-defined formats for exchanging various messages.

Protocol Data Unit (PDU)

A single unit of information transmitted among peer entities, containing protocol-specific control information and user data. In this context, user data includes the PDU of the next-highest layer of the communications stack.

Provider Service Identifier

An identifier of an application area. Used within certificates to establish permissions for end entities.


An identifier used by an individual that is not associated with the individual's identity, and may change to prevent such association.

Pseudonym Certificate

An authorization certificate (q.v.) that indicates its holder's permissions but not its holder's identity.


A property wherein an entity's permanent or long-lived identities, and its long-term patterns of behavior, cannot be deduced from its network traffic and are only observable by appropriately authorized parties.

Public Key

See Asymmetric Encryption Algorithm.

Public Safety

This area addresses the management by public safety agencies of emergencies or incidents in the transportation network including those relating to HAZMAT materials that are transported through the transportation network. It covers public safety (police, fire, and emergency medical services) agencies using emergency management services to improve their response to emergency situations. The area also addresses how emergency operations centers interact with transportation and public safety agencies to support response to disasters and for evacuations affecting the transportation network.

Public Transportation

This area addresses the management, operations, maintenance and security of public transportation to enable them to provide transit services that operate in a timely and efficient manner, delivering operational information, including multimodal information to the operators and users, This area covers both fixed route and demand response systems, as well as those passenger rail systems operated by transit agencies.

Purpose and Need

A description of the transportation problem (not solution) explaining the primary goal or reason for which a project is being pursued. The statement should be specific enough so that the range of alternatives developed will offer real potential solutions and should reflect priorities and limitations in the area such as environmental resources, growth management, land use planning, and economic development.