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Level of Service
Level of Service A
Level of Service A describes a condition of free flow, with low volumes and high speeds.
Level of Service B
Level of Service B is the zone of stable flow, with operating speeds beginning to be restricted somewhat by traffic conditions. Drivers still have reasonable freedom to select their speed and lane of operation.
Level of Service C
Level of Service C is still in the zone of stable flow, but speeds and maneuverability are more closely controlled by the higher volumes.
Level of Service D
Level of Service D approaches unstable flow, with tolerable operating speeds being maintained, though considerably affected by changes in operating conditions.
Level of Service E
Level of Service E cannot be described by speed alone, but represents operations at even lower operating speeds than in Level D, with volumes at or near the capacity of the highway.
Level of Service F
Level of Service F describes forced flow operation at low speeds, where volumes are below capacity.
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