A measure of time delay experienced in a system, the precise definition of which depends on the system and the time being measured. For a data element in this context, latency is the time difference between the time that data value is acquired by
the source and the time the message is transmitted.

Legacy System

Existing transportation systems, communications systems, and institutional processes.

Level of Service (LOS)

A measure of the quality of the operation of different roadway types defined in the Highway Capacity Manual (HCM). There are six LOS grades ranging from LOS A, representing optimum operation, to LOS F, representing congested or unstable flow.


A remote sensing method that uses light in the form of a pulsed laser to measure ranges (variable distances).

Life cycle

Evolution of a system, product, service, project or other human-made entity from conception through retirement.

Link (RF)

A communications channel being used in support of application data transfer needs.

Link (traffic)

A segment of a road network. While highway links are generally separated by one data collection node (such as an RSU or a vehicle detector station), local road links tend to be limited by intersections with cross streets. Other common usages of the
word "link," such as those used in telecommunications, may also appear in the architecture.

Long Distance Trips

Trips of 100 miles or more.

Long Range Goal

A long-term (20-50 years) end toward which programs and activities are ultimately directed.

Long Range Objective

A long-term (20-50 years) general end that is achievable and marks progress toward a goal.

Long Range Program Plan (LRPP)

A 5-year plan, updated annually, developed by each state agency to achieve state goals, agency program objectives and the service outcomes from those programs. It provides the framework for developing agency budget requests and related performance measures.

Long-Range Transportation Plan (LRTP)

Also referred to as the "Transportation Plan", a document resulting from regional or statewide collaboration and consensus on a region's or state's transportation system, and serving as the defining vision for the region's or state's transportation systems and services. In metropolitan areas, this is the official multimodal transportation plan addressing no less than a 20-year planning horizon that is developed, adopted, and updated by the MPO through the metropolitan transportation planning process.

Low Emissions Zone

A geographically defined area that seeks to restrict or deter access by specific categories of high-polluting vehicles to improve the air quality within the geographic
area. The low-emissions zone can be dynamic, allowing the operating entity to change the location, boundaries, or time of the low-emissions zone.

Lower Layers

The Access and TransNet Layers of the ARC-IT communications reference model, along with any related functionality of the Management and Security Entities. In some contexts, the lower layers may also include some generic aspects the Facilities Layer.