National ITS Architecture Glossary

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.

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

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.

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.

A document of the National Architecture that describes the transportation and communications layers resulting from the partitioning of the processes within the logical architecture, presents architecture flow diagrams that show data passing among physical subsystems, and provides characteristics and constraints on the data flows.

Entities are the persons, places, and things that make up an intelligent transportation system. In the physical architecture, an entity represents a National ITS Architecture subsystem or terminator.

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.

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.

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).

A function or activity identified in the logical architecture of the National ITS Architecture that is required to support the ITS user service requirements. The logical architecture 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"). General processes are defined in terms of more detailed processes using data flow diagrams. The most detailed processes (sometimes called primitives) are defined in Process Specifications (PSpecs).

The textual definition of the most detailed processes identified in the logical architecture of the National ITS Architecture. The process specification includes an overview, a set of functional requirements, and a complete set of inputs and outputs.

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.

A framework that identifies the institutional agreement and technical integration necessary to interface a major ITS project with other ITS projects and systems.