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Level of Service <br />* All intersections in Snoqualmie Pass are unsignalized intersections. The HCM has a different delay standard for signalized and roundabout controlled intersections. <br />† https://geo.wa.gov/datasets/WSDOT::wsdot-level-of-service-standard-for-state-routes/explore?location=47.416903%2C-121.417223%2C14.55 <br />‡ https://www.co.kittitas.wa.us/uploads/documents/cds/comp-plan/2021/2021%20Comprehensive%20Plan.pdf <br />Level of Service (LOS) is a metric used to <br />assess how well intersections function <br />by evaluating factors such as vehicle <br />delay, congestion, and overall traffic flow. <br />It provides a snapshot of operational <br />performance during periods of high <br />demand. <br />Due to the unique traffic patterns in Snoqualmie <br />Pass, intersection performance was analyzed during <br />peak hours on both weekdays and weekends. To <br />capture seasonal variation, data collection was <br />conducted in October, reflecting traffic during non- <br />snow conditions, and in February, reflecting traffic <br />during the ski season. <br />The LOS grading system ranges from A to F, <br />with each grade representing a different level of <br />congestion. An intersection operating at LOS A <br />signifies a smooth flow of traffic with minimal or no <br />delays. On the other hand, an intersection operating <br />at LOS F indicates severe congestion, causing <br />significant delays for vehicles and exceeding the <br />roadway's capacity. <br />Table 1 presents the definitions of each LOS grade <br />for unsignalized intersections* as established in the <br />Highway Capacity Manual (HCM) 7th Edition and <br />published by the Transportation Research Board in <br />2022. The HCM serves as a standardized approach <br />for evaluating vehicle operations. <br />WSDOT establishes LOS standards for state <br />highways and ferry routes of statewide significance <br />(HSS) under RCW 47.06.140(2). For SR 906, WSDOT <br />has identified an LOS C standard.† <br />Kittitas County’s 2021 Comprehensive Plan sets <br />LOS standards for its roadway network based on <br />geographic context. The County aims to maintain <br />LOS C in rural areas and LOS D in urban areas, with <br />Snoqualmie Pass classified as a rural area.‡ <br />Based on the traffic counts collected and current <br />intersection geometries, all intersections within <br />the study area operated at LOS A or B during <br />peak hours in October (representing non-snow <br />conditions). In February, which captures ski season <br />travel patterns and increased weekend congestion, <br />most intersections still operated at LOS B or better. <br />Only SR 906 & I-90 EB Off-Ramp dropped to LOS <br />C on weekends, still within the acceptable standard <br />set by WSDOT. These results do not apply to all <br />time periods. The study area’s roadway network is <br />relatively sparse, offering limited route options for <br />most travelers. As a result, the area roadway network <br />can be overwhelmed in the mornings as people <br />arrive to park for their day of winter sports, as well <br />as in the afternoon, as people leave for the day. <br />The rural network accommodates a mix of through <br />traffic, cars searching for a place to park, vehicles <br />parking, people walking from parked vehicles to <br />destinations, semi-trucks stopping to rest or access <br />services, and travelers that are unfamiliar with the <br />area, who sometimes make unpredictable or even <br />unsafe travel maneuvers. The friction that occurs <br />during these busy periods can impact safety and <br />mobility, as well as quality of life, particularly for <br />those who live and work in the Pass. In addition to <br />considering current conditions, the project team <br />Table 1. Level of Service Definitions <br />Level of Service Description <br />Control Delay (seconds/vehicle) <br />for Unsignalized Intersections <br />A Free-flowing conditions ≤ 10 <br />B Stable operating conditions 10-15 <br />C Stable operating conditions, but individual motorists <br />are affected 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, 7th Edition. <br />The following intersections were <br />evaluated (as shown in Figure 22): <br /> ƒSR 906 & I-90 EB Off Ramp (Location 1) <br /> ƒSR 906 & Guye Peak Lane (Location 2) <br /> ƒI-90 WB Off Ramp/I-90 WB On Ramp <br />& Yellowstone Trail Road (Location 4) <br /> ƒSR 906 & Tanner Way/Driveway (Location 6) <br /> ƒHyak Dr E & SR 906 & Driveway (Location 7) <br /> ƒSR 906 & I-90 EB Off Ramp/I-90 <br />EB On Ramp (Location 8) <br /> ƒSR 906 & I-90 WB Ramp (Location 9) <br />37 Snoqualmie Pass Comprehensive Safety Plan | Kittitas County