California Environmental Quality Act (CEQA) Transportation Assessment - Vehicle Miles Traveled (VMT) Analysis
Introduction to VMT Analysis Methodology
With the passage of Senate Bill 743 (SB 743), the way transportation impacts are assessed under CEQA shifted from level of service (LOS) analysis to vehicle miles traveled (VMT). For compliance with SB 743, a VMT analysis is necessary for land use projects that have the potential to increase baseline VMT per service population (total population plus employment) within the city. The main goal is to promote transportation efficiency by normalizing VMT per service population, providing a more comprehensive metric for evaluating transportation impacts.
The VMT analysis must follow methodologies and assumptions approved by the City Traffic Engineer. To guide this process, a flowchart outlining the VMT analysis procedure (referred to as "Attachment A: VMT Analysis Flowchart") is available, along with a web-based tool designed to assist with VMT screening and mitigation (Attachment B: SGVCOG VMT Assessment Tool Users Guide). The key steps in VMT analysis include project screening, determining project impact, and conducting forecasting for non-screened projects.
VMT Project Screening Process
Screening is a crucial first step in determining whether a detailed VMT analysis is required. Three types of screening methods are typically applied to evaluate if a project may be exempt from project-level VMT assessments. These are:
- Transit Priority Area (TPA) Screening
- Low VMT Area Screening
- Project Type Screening
Step 1: Transit Priority Area (TPA) Screening
Projects located within a Transit Priority Area (TPA) are presumed to have a less-than-significant impact on VMT unless there is substantial evidence to the contrary. TPAs are defined as areas within half a mile of a major transit stop or along a high-quality transit corridor, as specified under California law. However, a project might not qualify for this presumption if:
- The project has a Floor Area Ratio (FAR) less than 0.75.
- It includes more parking than required by the city.
- It is inconsistent with the city’s Sustainable Communities Strategy (SCS).
- The project replaces affordable housing units with fewer market-rate units.
Analysts are required to consult TPA maps available in the SGVCOG VMT assessment tool and confirm that no significant changes in transit service have occurred in the area before applying the TPA screening.
Step 2: Low VMT Area Screening
If a residential or office project is located in an area that generates low VMT (compared to regional averages), it is presumed to have a less-than-significant VMT impact. This presumption also applies to other employment-related and mixed-use developments, provided their VMT per resident, worker, or service population aligns with the existing land uses in that area.
Low VMT areas are identified using the SCAG travel forecasting model, which estimates VMT for specific Traffic Analysis Zones (TAZs). If a project’s land uses could increase the length or rate of vehicle trips, this presumption may not apply. Analysts use the SGVCOG VMT Evaluation Tool to determine if a project falls within a low VMT-generating area.
Step 3: Project Type Screening
Certain types of local-serving projects are assumed to have a less-than-significant impact on VMT. These include:
- Local-serving K-12 schools
- Local parks
- Daycare centers
- Retail developments under 50,000 square feet
- Local-serving hotels and assembly uses (e.g., places of worship)
- Senior housing and affordable housing
- Projects that generate fewer than 110 daily vehicle trips (e.g., 11 single-family homes or 10,000 square feet of office space)
Local-serving retail projects, for instance, often reduce VMT by bringing services closer to residential areas. The determination of a local-serving use must demonstrate that it caters primarily to existing residents and visitors in the community, not creating new demand but serving existing needs.
VMT Assessment for Non-Screened Projects
If a project is not exempt through screening, a detailed VMT analysis must be conducted. This requires forecasting VMT generated by the project using either the SCAG regional travel model or an appropriate sub-area model, subject to approval by the City Traffic Engineer.
Baseline Conditions
The baseline VMT represents the existing travel behavior at the time the Notice of Preparation (NOP) is issued for the environmental review. This data can be obtained from the SCAG model or sub-area models, and may require interpolation between base-year and future-year model scenarios.
Baseline Plus Project
In this scenario, the proposed project’s land uses are added to the baseline model. The objective is to estimate the VMT generated by the project, both for the project area and across the regional network. The results are compared to thresholds of significance to determine whether the project’s impact on VMT is significant.
The SGVCOG VMT assessment tool offers an estimate for "Baseline plus Project" conditions, but a full model run is recommended for accuracy and consistency.
Cumulative No Project
This scenario represents the future year VMT conditions in the absence of the project, accounting for projected population and employment growth. Cumulative data is available from the SCAG model.
Cumulative Plus Project
The "Cumulative plus Project" scenario assesses the impact of adding the project to future year conditions. If the project is large enough to influence the distribution of land uses across the region, a reallocation of land uses within the model may be required. If the project land uses are simply added to the model without adjusting for other developments, the analysis should acknowledge potential overestimation of the project's effect on VMT.
VMT Metrics and Thresholds of Significance
The analysis should include both total VMT and VMT per service population, which serves as the recommended metric for transportation impact analysis. Total VMT is also necessary for assessing air quality, greenhouse gas (GHG) emissions, and energy consumption.
Projects are assessed against thresholds of significance based on the citywide average VMT per service population. If the project-generated VMT exceeds the threshold, the project may be deemed to have a significant impact, triggering the need for mitigation.
Extracting VMT Data
VMT data is extracted from the travel demand forecasting model using the origin-destination trip matrix, which provides detailed information about vehicle trips generated by the project. In certain cases (e.g., for retail or office projects), it may be appropriate to isolate specific trip types, such as home-based work trips, to evaluate commute VMT.
Mitigation and Impact Reduction Strategies
If a project is found to have a significant VMT impact, mitigation measures must be considered. Common mitigation strategies include:
- Enhancing access to transit.
- Providing infrastructure for active transportation (e.g., biking, walking).
- Encouraging mixed-use development to reduce the need for long vehicle trips.
- Implementing transportation demand management (TDM) measures, such as carpool programs or telecommuting incentives.
The City Traffic Engineer must approve any mitigation strategies, and their effectiveness must be evaluated to ensure compliance with CEQA.
VMT analysis under SB 743 represents a fundamental shift in how transportation impacts are evaluated in California. By focusing on reducing overall vehicle travel and encouraging more efficient land use patterns, this approach supports the state’s goals for sustainability, climate action, and improving quality of life. The screening methods and VMT forecasting procedures outlined in this document provide a clear pathway for assessing the transportation impacts of land use projects, helping cities like Diamond Bar navigate the complexities of CEQA compliance.
With the growing emphasis on transportation efficiency, the VMT analysis process ensures that future development aligns with state and regional goals for reducing greenhouse gas emissions and improving transportation sustainability
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