Los Angeles County Traffic Study Guidelines Section 3.1.4.2: Project Impact Determination
Residential Projects:
- Estimations: Daily vehicle trips, daily VMT, and daily residential VMT per capita for residential projects should be estimated using the SCAG RTP/SCS Travel Demand Forecast Model (as described in the Los Angeles County Senate Bill (SB) 743 Implementation and CEQA Updates Report).
- Considerations: Include transportation demand management (TDM) strategies as project design features in the estimation of daily vehicle trips and VMT (refer to Section 3.1.5 for TDM strategies).
Office Projects:
- Estimations: Daily vehicle trips, daily VMT, and daily employment VMT per employee for office projects should be estimated using the SCAG RTP/SCS Travel Demand Forecast Model (as described in the Los Angeles County Senate Bill (SB) 743 Implementation and CEQA Updates Report).
- Considerations: Include TDM strategies as project design features in the estimation of daily vehicle trips and VMT.
Regional Serving Retail Projects: The Scoping Document prepared by the project applicant and Public Works will outline one of the following methods for impact determination:
- Market-Study-Based Transportation Analysis:
- Demonstrate that the project area is underserved for the proposed retail use and that the project will shorten existing shopping trips by creating an intervening location between trip origins and current retail destinations.
- SCAG RTP/SCS Travel Demand Forecasting Model:
- Run the model with and without the project. The total number of trips will not be materially influenced by the additional retail space, but the model will redistribute home-shopping trips from other retail destinations to the proposed retail destination.
- If the project is entirely retail:
- Determine the traffic analysis zone (TAZ) in which the project is located.
- Convert the project retail land uses into appropriate employment categories used in the model and adjust the socioeconomic parameters in the TAZ to reflect the removal of existing land uses and the addition of the project.
- Run the four-step model process for the model existing base year for four time periods (AM peak, midday, PM peak, nighttime) for the base (“no project”) and “plus project” scenarios.
- Calculate total VMT for each time period, sum to determine daily VMT for each scenario, and subtract the base scenario VMT from the “plus project” scenario VMT to determine the net change in daily VMT.
- For mixed-use developments including more than 50,000 square feet of retail:
- Create a “without retail” model scenario including the rest of the project’s proposed land uses.
- Run the four-step model for this “with retail” scenario and subtract the “without retail” scenario VMT from the “with retail” scenario VMT to determine the net change in daily VMT.
Land Use Plans:
- Estimations: Daily vehicle trips, daily VMT, and daily total VMT per service population (residents and employees) should be estimated using the SCAG RTP/SCS Travel Demand Forecast Model (as described in the Los Angeles County Senate Bill (SB) 743 Implementation and CEQA Updates Report).
- Considerations: Include TDM strategies as project design features in the estimation of daily vehicle trips and VMT.
Unique Land Uses:
- For projects that do not fit into the categories above, a customized approach may be required to estimate daily trips and VMT.
- Methodology: Develop the methodology and thresholds in consultation with and approved by Public Works staff at the outset of the study.
Mixed-Use Projects:
- The project VMT impact is considered significant if any (one or all) of the project land uses exceed the impact criteria for that particular land use, taking credit for internal capture.
Mitigation: Consider mitigation options that reduce the VMT generated by any or all of the land uses.
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