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Table 31-1. Level of Service Descriptions <br /> Level of Type of Control Delay(SecondsNehicle) <br /> Service Flow Delay Maneuverability Signalized Unsignalized All-Way Stop <br /> A Stable Very slight delay. Progression is very favorable, with Turning movements are easily < 10.0 < 10.0 < 10.0 <br /> Flow most vehicles arriving during the green phase not made,and nearly all drivers <br /> stopping at all. find freedom of operation. <br /> B Stable Good progression and/or short cycle lengths. More Vehicle platoons are formed. >10 and<20.0 >10 and< 15.0 >10 and< 15.0 <br /> Flow vehicles stop than for LOS A,causing higher levels of Many drivers begin to feel <br /> average delay. somewhat restricted within <br /> groups of vehicles. <br /> C Stable Higher delays resulting from fair progression and/or Back-ups may develop behind >20 and<35.0 >15 and<25.0 >15 and<25.0 <br /> Flow longer cycle lengths. Individual cycle failures may turning vehicles. Most drivers <br /> begin to appear at this level. The number of vehicles feel somewhat restricted <br /> stopping is significant,although many still pass <br /> through the intersection without stopping. <br /> D Approac The influence of congestion becomes more noticeable. Maneuverability is severely >35 and<55.0 >25 and<35.0 >25 and<35.0 <br /> hing Longer delays may result from some combination of limited during short periods <br /> Unstable unfavorable progression,long cycle lengths,or high due to temporary back-ups. <br /> Flow volume-to-capacity ratios. Many vehicles stop,and <br /> the proportion of vehicles not stopping declines. <br /> Individual cycle failures are noticeable. <br /> E Unstable Generally considered to be the limit of acceptable There are typically long >55 and<80.0 >35 and<50.0 >35 and<50.0 <br /> Flow delay. Indicative of poor progression,long cycle queues of vehicles waiting <br /> lengths,and high volume-to-capacity ratios. upstream of the intersection. <br /> Individual cycle failures are frequent occurrences. <br /> F Forced Generally considered to be unacceptable to most Jammed conditions. Back-ups >80.0 >50.0 >50.0 <br /> Flow drivers. Often occurs with over saturation. May also from other locations restrict or <br /> occur at high volume-to-capacity ratios. There are prevent movement. Volumes <br /> many individual cycle failures. Poor progression and may vary widely,depending <br /> long cycle lengths may also be major contributing principally on the downstream <br /> factors. back-up conditions. <br /> Source: Highway Capacity Manual,Fourth Edition,Transportation Research Board,2000. <br />