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Traffic Impact Analysis: Study Scenarios, Data Collection, and Forecasting Methodologies for the project in the City of Murrieta

4.0 STUDY AREA BOUNDARIES FOR LEVEL OF SERVICE (LOS) ASSESSMENT

The study area for a Level of Service (LOS) assessment must be carefully defined to ensure a comprehensive understanding of the transportation impacts of a proposed project. At a minimum, the study must encompass all intersections where a "Collector" or higher classification street intersects with another "Collector" or higher classification street and where the proposed project is expected to generate 50 or more peak-hour trips. This threshold ensures that all significant traffic impact locations are adequately evaluated.

While the default study area should not exceed a five-mile radius from the project site, exceptions may be made when justifiable evidence supports the need for an expanded scope. Such justifications may include broader regional impacts, connections to major freeway corridors, or local agency directives. The City Department of Public Works/Engineering reserves the right to adjust the study area boundaries based on site-specific conditions, anticipated traffic impacts, or at its discretion. This flexibility ensures that analyses remain relevant and appropriately scaled to actual project influence.

5.0 ANALYSIS SCENARIOS

To provide a robust and accurate assessment of intersection capacity and roadway segment performance, traffic studies must include multiple analysis scenarios. These scenarios account for varying conditions over time and help identify potential mitigation measures to maintain acceptable traffic operations. The required scenarios include:

a) Existing Conditions: This scenario represents the current traffic conditions without any new development. It serves as a baseline for comparison against other scenarios.

b) Background Conditions: Defined as the opening year conditions with traffic generated by already approved projects in the area. If no significant approved projects exist, an ambient growth rate may be applied instead of assigning specific traffic volumes from other projects.

c) Background Plus Project Conditions: This scenario builds upon the background conditions by adding traffic generated by the proposed project. It helps evaluate the direct impact of the project under near-term conditions.

d) Cumulative No Project Conditions: This scenario projects traffic growth to a long-term horizon (typically aligned with the forecast horizon of the RIVTAM/RIVCOM travel demand forecasting model) and includes traffic from approved and pending projects within the study area. The goal is to assess the future transportation network performance without the proposed project.

e) Cumulative Plus Project Conditions: This scenario incorporates the proposed project’s traffic into the cumulative conditions, allowing planners to understand its long-term impact on the transportation system.

All developments within the study area that have received formal approval (including approved development plans, tentative tract maps, and conditional use permits) must be incorporated into cumulative traffic assessments. Additionally, proposed but not yet approved projects may be included at the discretion of the City. To account for background growth, the Engineering Department will specify an ambient growth rate that should be applied to existing traffic volumes.

Phased Project Assessments

For projects that are implemented in phases, the LOS assessment can be conducted using one of three approaches:

  1. Phased Trigger Analysis: Identifying the specific phase that triggers a necessary traffic improvement by comparing background conditions with background plus project conditions.

  2. Incremental Phase Evaluation: Conducting separate assessments for the opening year of each phase to ensure incremental impacts are properly addressed.

  3. Comprehensive Initial Analysis: Evaluating the entire project in one study, followed by subsequent traffic studies for each phase to confirm that required improvements are implemented at appropriate times.

The City should be consulted on the most suitable approach, though the phased trigger analysis is recommended for most projects.

6.0 DATA COLLECTION, PROJECT TRIP GENERATION, AND FORECASTING METHODOLOGIES

Maintaining consistency across Traffic Impact Analyses (TIAs) requires adherence to standardized data collection, trip generation, and forecasting methodologies. These methodologies align with current industry best practices and ensure reliable results.

Traffic Counts

To establish existing traffic conditions, data must be collected following these guidelines:

  • Conduct peak-period turning movement counts at all study intersections, required roadway segments, and relevant driveways. Bicycle and pedestrian counts must be included at intersections with high non-motorized travel activity.

  • Heavy vehicle percentages should be explicitly counted at intersections with significant truck traffic.

  • Average Daily Traffic (ADT) volumes should be recorded for all roadways within the study area, including vehicle classification counts where heavy vehicle use is substantial.

  • Traffic count data should not be older than one year unless explicitly approved by the City.

  • Data collection should avoid holiday weeks, non-school session periods, and the timeframe between Thanksgiving and the first week of the new year unless otherwise approved.

  • Counts should be conducted on Tuesdays, Wednesdays, or Thursdays to capture typical traffic patterns.

  • In congested conditions, queue lengths should be recorded at 15-minute intervals.

  • Unless directed otherwise, counts should be taken during:

    • Morning peak (7:00 a.m. - 9:00 a.m.)

    • Evening peak (4:00 p.m. - 6:00 p.m.)

    • Midday or school-release peak (if required by the City)

    • Additional periods, such as off-peak, weekend, or special event conditions, may be required based on the project type.

All traffic count data should be included in the study appendices.

Trip Generation

Trip generation estimates must be derived from local trip generation surveys conducted at a minimum of three similar project sites using methodologies outlined in the Institute of Transportation Engineers (ITE) Trip Generation Handbook. If valid local data is unavailable, ITE trip rates may be used with full disclosure of any limitations, particularly regarding land use context.

Projects with significant truck traffic (e.g., high-cube warehouses, logistics hubs) must consult with the City for customized trip generation methodologies. The proposed trip generation methodology must be documented in the scoping form for City review and approval prior to the study’s initiation.

For mixed-use developments, trip internalization should be calculated using state-of-the-practice methodologies, such as the EPA’s MXD model or ITE’s mixed-use trip generation approach. Internalization calculations, including input assumptions (e.g., intersection density, transit-oriented development status, total acreage), must be clearly documented.

For capacity analyses, all truck trips should be converted into passenger car equivalents (PCE), or the heavy vehicle percentage should be adjusted accordingly.

Trip Distribution

Trip distribution should be based on expected origin-destination patterns for the proposed land use. Preferred methodologies include:

  • Mobile device data from at least three comparable locations to measure trip distribution patterns.

  • Select zone assignments from the RIVCOM model.

  • Supporting data, including:

    • Proximity to employment, commercial, and recreational centers.

    • Existing link and turning movement volumes.

    • ADT data.

    • Accessibility to regional transportation corridors.

    • Local and regional traffic circulation characteristics.

A preliminary trip distribution map must be submitted in the scoping form for City review and approval. The City may further refine trip distribution based on:

  • Project type and scale.

  • Local roadway conditions.

  • Similar land uses nearby.

  • Designated truck routes.

  • Additional City guidance.

Trip Forecasting

For cumulative conditions, future traffic volume projections must be based on the adopted Riverside County Travel Demand Model or the City of Murrieta’s traffic model. Prior to model execution, the study preparer must review land use allocations in the study area to ensure alignment with available land supply, previously approved projects, the General Plan, and applicable zoning.

By implementing these methodologies, the City ensures a standardized, data-driven approach to evaluating transportation impacts. This approach enables decision-makers to develop effective mitigation strategies, promote sustainable mobility, and maintain efficient traffic operations as development.


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