In general terms, LOS is a classification system used to describe the quality of the mobility provided by a transportation system. It is an alphabetical grading system that provides a measurement of the number of vehicles a roadway can accommodate over a given period of time. The concept of LOS has been used by traffic and transportation engineers for nearly 50 years to describe conditions for automobile travel on existing or future roadways.
Until recently, transportation engineering and planning in the United States has focused primarily around the movement of the automobile. Roadways were designed and subsequently evaluated based on their performance from the perspective of an automobile driver. LOS became the widely accepted methodology for measuring the performance of such roadways, which worked in the favor of motor vehicle travel, often at the expense of other roadway users.
