Basic Freeway Section-- Freeway segments that are outside of the influence of ramps or weaving sections.

Capacity-- The maximum number of vehicles that can reasonably be expected to traverse over a specific section of roadway, in one direction, during a given time period and under the prevailing conditions. This is expressed in passengers cars per hour per lane (pcphpl).

Design Conditions-- The physical qualities of a basic freeway section such as lane width, shoulder clearances and density of interchanges (on and off ramps).

Density-- The number of vehicles in a one-mile segment of one lane of traffic.

Flow rate-- The rate, in vehicles per hour or passenger cars per hour, at which traffic traverses a freeway segment.

Free-flow speed-- The speed of traffic flow that is unaffected by upstream or downstream conditions. Ideally, free-flow speed is the speed that occurs when density and flow are zero.

Level of Service (LOS)-- A measure of the operating conditions of a basic freeway section. There are six categories – A through F – with F being the least desirable.

Peak-hour factor-- The ratio of the number of vehicles during the peak hour to four times the number of vehicles entering the traffic stream during the peak 15-minute period.

Traffic conditions-- The qualities of traffic such as traffic speed, density, vehicle types and traffic flow rate.