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TABLE 9-1 <br />LEVEL OF SERVICE CRITERIA FOR SIGNALIZED INTERSECTIONS (HCM)18 <br />Level of Service <br />(LOS) <br />Control Delay Per Vehicle <br />(seconds/vehicle) <br />Level of Service Description <br />This level of service occurs when progression <br />is extremely favorable and most vehicles arrive <br />A <br />< 10.0 <br />during the green phase. Most vehicles do not <br />stop at all. Short cycle lengths may also <br />contribute to low delay. <br />This level generally occurs with good <br />B <br />> 10.0 and < 20.0 <br />progression, short cycle lengths, or both. More <br />— <br />vehicles stop than with LOS A, causing higher <br />levels of average delay. <br />Average traffic delays. These higher delays <br />may result from fair progression, longer cycle <br />lengths, or both. Individual cycle failures may <br />C <br />> 20.0 and < 35.0 <br />begin to appear at this level. The number of <br />vehicles stopping is significant at this level, <br />though many still pass through the intersection <br />without stopping. <br />Long traffic delays. At level D, the influence <br />of congestion becomes more noticeable. <br />Longer delays may result from some <br />D <br />> 35.0 and < 55.0 <br />combination of unfavorable progression, long <br />— <br />cycle lengths, or high v/c ratios. Many vehicles <br />stop, and the proportion of vehicles not <br />stopping declines. Individual cycle failures are <br />noticeable. <br />Very long traffic delays. This level is <br />considered by many agencies (i.e. SANBAG) <br />to be the limit of acceptable delay. These high <br />E <br />> 55.0 and < 80.0 <br />delay values generally indicate poor <br />progression, long cycle lengths, and high v/c <br />ratios. Individual cycle failures are frequent <br />occurrences. <br />Severe congestion. This level, considered to be <br />unacceptable to most drivers, often occurs with <br />over saturation, that is, when arrival flow rates <br />F <br />>_ 80.0 <br />exceed the capacity of the intersection. It may <br />also occur at high v/c ratios below 1.0 with <br />many individual cycle failures. Poor <br />progression and long cycle lengths may also be <br />major contributing factors to such delay levels. <br />18 Source: Highway Capacity Manual (Signalized Intersections). <br />