Non-CEQA Transportation Assessment: Level of Service Analysis Procedure
Traffic analyses for the City of Diamond Bar must be conducted by a registered traffic engineer, civil engineer, or qualified transportation planner. The analyst and project applicant must collaborate with City Planning and Public Works staff to define the study area, assumptions, and methodologies. All assumptions and methodologies, including the Level of Service (LOS) analysis, are subject to approval by the City Traffic Engineer.
Traffic Counts
Traffic counts older than two years require City Traffic Engineer approval; otherwise, new counts must be collected by a qualified firm. Turning movement data should be gathered in 15-minute intervals during the specified peak hours unless otherwise directed. Traffic counts should be conducted on days of good weather, typically on Tuesdays through Thursdays, while schools are in session.
Trip Generation
The latest ITE Trip Generation Manual rates will be used for determining project trip generation, with support required for any alternative sources. Justification for trip generation credits, such as pass-by traffic, must be provided and based on reliable data or approved studies.
Trip Distribution and Assignment
Trip distribution and assignment must be clearly outlined and approved by the City Traffic Engineer, using demographic and regional data. Assignments should reflect current and future roadway networks.
Traffic Forecasts
Analyses must include traffic forecasts at project buildout, incorporating cumulative project impacts. The SCAG Travel Demand Model or an appropriate sub-area model should be used for projections, with confirmation that nearby projects are included.
Analysis Methodologies
The City uses the Highway Capacity Manual (HCM) methodology for evaluating AM and PM peak hour LOS. Specific parameters, such as saturation flow rate, cycle lengths, and peak hour factors, must be based on field data or guidelines. Pedestrian activity impacts on flow rates should be assessed case by case.
Transportation Effects
The City’s General Plan requires intersections to operate at LOS D or better. Signalized intersections requiring improvements are identified if project traffic causes deterioration to LOS E or F, or if the volume-to-capacity ratio increases by 0.010 or more at an intersection already operating at LOS E or F.
Unsignalized intersections require improvements if project traffic degrades operations to LOS E or F and meets peak hour signal warrants.
Analysis Scenarios
The LOS analysis should evaluate existing conditions, opening year (with and without the project), horizon year, and horizon year plus project scenarios. Projects with multiple phases require interim year analysis.
On-Site Parking Analysis
Parking supply versus City code requirements must be addressed, including details for mixed-use developments. Justification for any parking reduction must be provided, and shared parking evaluations may be considered.
Access and Circulation Analysis
The analysis should address access points, spacing between driveways and intersections, potential signalization, stacking distances, sight distance, pedestrian connections, and any other operational characteristics identified by City staff.
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