Intersections are typically the main constraint on vehicle capacity in a transportation network. Therefore, these guidelines focus on intersection evaluation. However, in some cases, analyzing roadway segments may be appropriate and could be requested by the County Transportation Department. The following sections outline the methodology for evaluating roadway segments when required.
Analysis Methodology
Daily roadway segment analysis should use thresholds from the latest edition of the Transportation Research Board's Highway Capacity Manual (HCM 6th Edition), which reflects the current state of the practice. The HCM methodology assigns a Level of Service (LOS) grade to a roadway segment based on whether daily volumes exceed specific thresholds.
General Plan Consistency Requirements
Consistent with the acceptable LOS for the Desert, Valley, and Mountain regions as described in the current General Plan, the County should consider the following thresholds and improvement requirements for roadway segments:
- Any study roadway segment in the Valley or Mountain regions that operates at an LOS D or better without project traffic, where the addition of project traffic causes the segment to degrade to an LOS E or F, should identify improvements to achieve LOS D.
- Any study roadway segment in the Desert region that operates at an LOS C or better without project traffic, where the addition of project traffic causes the segment to degrade to an LOS D, E, or F, should identify improvements to achieve LOS D.
- Any roadway segment that operates unacceptably in the no-project scenario, where the project adds traffic exceeding 5% of the roadway capacity (e.g., a volume-to-capacity ratio increase of 0.05), should identify improvements to increase capacity on the segment.
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