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Appendix F: Level of Service (LOS) <br />CONSULTING Research Brief <br />Volume No. 3 <br />Level of Service (LOS) <br />Level of Service (LOS) is a qualitative description, similar to typical school grades, that traffic engineers use to communi- <br />cate how good or bad traffic operations are on a corridor, intersection, or interchange. <br />Common Factors <br />Traffic can be a hard thing to quantify as everyone has a <br />different tolerance for congestion. What seems excessively <br />long to one person may seem good enough for another. <br />These differences are readily apparent when comparing <br />small towns or rural areas, where five cars an hour can <br />be the norm, to big cities or downtowns, where less than <br />hundred cars an hour, even in the middle of night, is rare. <br />To combat this issue and provide a consistent measuring <br />tool for traffic studies, a "Level of Service" rating was <br />developed. Level of Service ratings are based on the <br />roadway or intersection characteristics and the amount of <br />traffic. Just like grade school, LOS A represents the best <br />traffic operations, where traffic flows freely. LOS F, on the <br />other hand, represents failing operations, where the road <br />or intersection is congested and running beyond maximum <br />capacity. LOS E is typically considered "at capacity" which <br />means the amount of traffic is right at the level the roadway <br />or intersection can adequately accommodate. Using Level <br />of Service letter grades provides an easy way to convey <br />road operations to the general public and has been adopted <br />across the United States. <br />Common Factors Impacting Level of <br />Service <br />• Number of Lanes. <br />• Traffic Volumes. <br />• Intersection Control (stop sign, signal, roundabout, <br />interchange.) <br />• Amount of access on a corridor. <br />• Percentage of turning traffic. <br />•Traffic signal cycle length (green time devoted to each <br />approach) and phasing (one green for all approach <br />movements or separate green arrows.) <br />• Percentage of heavy trucks. <br />• Roadway Grades. <br />• Distribution of traffic within a peak hour as well as over the <br />course of a day. <br />• Pedestrian activity. <br />• Bicycle activity. <br />Level of Service criteria have been developed for multiple <br />types of traffic operations including: <br />• Intersections <br />• Urban Corridors <br />• Freeways <br />• Transit Service <br />• Bicycle Operations <br />• Pedestrian Operations <br />The most common LOS criteria used is for car operations <br />at intersections; both signalized and unsignalized. For an <br />intersection Level of Service analysis, average delay for <br />cars travelling through the intersection is used to determine <br />the appropriate grade. A high delay results in a poor LOS <br />rating and equates to poor operations. Similarly, low delay <br />results in a good LOS rating and equates to good or great <br />operations. <br />LOS can be determined for the intersection as a whole, or <br />for individual movements. It is common during peak periods <br />in major population areas for an intersection to have an <br />acceptable overall LOS rating, but fail to achieve a good <br />grade for individual movements. <br />90' <br />80 <br />�fl <br />Jr; 60 <br />e 50 <br />10 <br />30 <br />20 <br />10 <br />0 <br />LOS O <br />iJnsigna4zed <br />Inter sect Enn <br />LOSO <br />LOSc <br />S1E5.58zed <br />Intersection <br />Traffic Impact Study Pearson Farm Residential Development F1 Spack Consulting <br />