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Appendix G | 2 <br /> <br />Overview <br />Level of Service (LOS) at intersections is a standardized measure used to evaluate how efficiently an <br />intersection handles traffic. <br />The LOS grading system ranges from A to F, with each grade representing a different level of <br />congestion. An intersection operating at LOS A signifies a smooth flow of traffic with minimal or no <br />delays. On the other hand, an intersection operating at LOS F indicates severe congestion, causing <br />significant delays for vehicles and exceeding the roadway's capacity. <br />Table 1 presents the definitions of each LOS grade for unsignalized intersections 1 as established in the <br />Highway Capacity Manual (HCM) Sixth Edition and published by the Transportation Research Board <br />in 2016. The HCM serves as a standardized approach for evaluating the operational performance of <br />roadway segments. <br />Table 1: Level of Service Definitions <br />Level of <br />Service Description <br />Control Delay <br />(seconds/vehicle) <br />For unsignalized <br />intersections <br />A Free-flowing conditions ≤ 10 <br />B Stable operating conditions 10-15 <br />C Stable operating conditions, but individual motorists are affected <br />by the interaction with other motorists 15-25 <br />D High density of motorists, but stable flow 25-35 <br />E Near-capacity 35-50 <br />F Over capacity, with delays ≥ 50 <br />Source: Highway Capacity Manual, 6th Edition <br />WSDOT establishes LOS standards for state highways and ferry routes of statewide significance <br />(HSS) under RCW 47.06.140(2). For SR 906, WSDOT has identified an LOS standard of C. 2 <br />Kittitas County’s 2021 Comprehensive Plan sets LOS standards for its roadway network based on <br />geographic context. The County aims to maintain LOS C in rural areas and LOS D in urban areas. 3 <br />Methodology & Data Collection <br />Due to the unique travel patterns in Snoqualmie Pass, data collection was conducted during peak <br />hours on both weekdays and weekends to capture typical and recreational traffic volumes. To <br /> <br />1 All intersections in Snoqualmie Pass are unsignalized intersections. The HCM has a different delay standard for <br />signalized and roundabout controlled intersections. <br />2 https://geo.wa.gov/datasets/WSDOT::wsdot-level-of-service-standard-for-state- <br />routes/explore?location=47.416903%2C-121.417223%2C14.55 <br />3 https://www.co.kittitas.wa.us/uploads/documents/cds/comp-plan/2021/2021%20Comprehensive%20Plan.pdf <br />