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What is Level of Service (LOS) in Traffic?

June 1, 2024

Level of Service (LOS) is a quality measure describing operational conditions within a traffic stream, generally in terms of such service measures as speed and travel time, freedom to maneuver, traffic interruptions, and comfort and convenience.

The Higway Capacity Manual defines six LOS for each type of facility that has analysis procedures available. Letters designate each level, from A to F, with LOS A representing the best operating conditions and LOS F the worst. Each level of service represents a range of operating conditions and the driver's perception of those conditions. Safety is not included in the measures that establish service levels.

Level of service General operating conditions
A Free flow
B Reasonably free flow
C Stable flow
D Approaching unstable flow
E Unstable flow
F Forced or breakdown flow

General Definitions of Levels of Service (LOS), more specific definitions are defined in the HCM.

Related Terms:

Further Reference:

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