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TABLE 12-1 <br />LEVEL OF SERVICE CRITERIA FOR SIGNALIZED INTERSECTIONS (HCM 6 METHODOLOGY)' <br />Level of Service <br />Control Delay Per Vehicle <br />(LOS) <br />(seconds/vehicle) <br />Level of Service Description <br />This level of service occurs when progression is <br />A <br />< 10.0 <br />extremely favorable and most vehicles arrive during the <br />— <br />green phase. Most vehicles do not stop at all. Short cycle <br />lengths may also contribute to low delay. <br />This level generally occurs with good progression, short <br />B <br />> 10.0 and < 20.0 <br />cycle lengths, or both. More vehicles stop than with LOS <br />A, causing higher levels of average delay. <br />Average traffic delays. These higher delays may result <br />from fair progression, longer cycle lengths, or both. <br />C <br />> 20.0 and < 35.0 <br />Individual cycle failures may begin to appear at this level. <br />— <br />The number of vehicles stopping is significant at this <br />level, though many still pass through the intersection <br />without stopping. <br />Long traffic delays At level D, the influence of <br />congestion becomes more noticeable. Longer delays may <br />D <br />> 35.0 and < 55.0 <br />result from some combination of unfavorable progression, <br />— <br />long cycle lengths, or high v/c ratios. Many vehicles stop <br />and the proportion of vehicles not stopping declines. <br />Individual cycle failures are noticeable. <br />Very long traffic delays This level is considered by many <br />agencies to be the limit of acceptable delay. These high <br />E <br />> 55.0 and < 80.0 <br />delay values generally indicate poor progression, long <br />cycle lengths and high v/c ratios. Individual cycle failures <br />are frequent occurrences. <br />Severe congestion This level, considered to be <br />unacceptable to most drivers, often occurs with over <br />saturation, that is, when arrival flow rates exceed the <br />F <br />>_ 80.0 <br />capacity of the intersection. It may also occur at high v/c <br />ratios below 1.0 with many individual cycle failures. Poor <br />progression and long cycle lengths may also be major <br />contributing factors to such delay levels. <br />9 Source: Highway Capacity Manual 6, Chapter 19: Signalized Intersections. <br />75B-113 <br />