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chapter6_notes_ - 1 Chapter 6 Highway Capacity and Level of...

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1 Chapter 6 Highway Capacity and Level of Service Analysis Seek to measure Highway Performance (Congestion). Needed for: ± Highway construction ± Congestion relief Problems: ± Wide variation of highway conditions: Different roadway types (Freeway, multilane, etc.) Number of lanes and width of lanes Vehicle mix (cars vs. trucks) Shoulder widths Temporal variation in traffic flow over the day and over the peak hour 6.1 LEVEL OF SERVICE CONCEPT The level of service provides a qualitative ranking of the traffic operational conditions experienced by users of a facility Highway Capacity Manual defines the LOS categories for freeways and multilane highways as follows: Level of Service A free-flow conditions (traffic operates at free flow speeds as defined in Chapter 5). Individual users are virtually unaffected by the presence of others in the traffic stream. Freedom to select desired speeds and to maneuver within the traffic stream is extremely high. The general level of comfort and convenience provided to drivers is excellent. Level of Service B allows speeds at or near free-flow speeds, but the presence of other users in the traffic stream begins to be noticeable. Freedom to select desired speeds is relatively unaffected, but there is a slight decline in the freedom to maneuver within the traffic stream relative to LOS A. Level of Service C speeds at or near free-flow speeds, but the freedom to maneuver is noticeably restricted (lane changes require careful attention on the part of drivers). The general level of comfort and convenience declines significantly at this level. Disruptions in the traffic stream, such as an incident (for example, vehicular accident or disablement), can result in significant queue formation and vehicular delay. In contrast, the effect of incidents at LOS A or LOS B are minimal, and cause only minor delay in the immediate vicinity of the event. Level of Service D conditions where speeds begin to decline slightly with increasing flow. The freedom to maneuver becomes more restricted and drivers experience reductions in physical and psychological comfort. Incidents can generate lengthy queues because the higher density associated with this LOS provides little space to absorb disruption in the traffic flow. Level of Service E LOS E represents operating conditions at or near the roadway’s capacity. Even minor disruptions to the traffic stream, such as vehicles entering from a ramp or
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2 vehicles changing lanes, can cause delays as other vehicles give way to allow such maneuvers. In general, maneuverability is extremely limited and drivers experience considerable physical and psychological discomfort. Level of Service F
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chapter6_notes_ - 1 Chapter 6 Highway Capacity and Level of...

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