Overview
Senate Bill (SB) 743, signed in 2013, introduced a fundamental shift in transportation impact analysis under the California Environmental Quality Act (CEQA). The focus moved from measuring impacts on drivers, typically gauged through Level of Service (LOS), to assessing the environmental consequences of driving, measured via Vehicle Miles Traveled (VMT). This transition supports state goals of reducing greenhouse gas (GHG) emissions, encouraging infill development, and promoting public health through active transportation.
In January 2019, the California Natural Resources Agency formalized updates to CEQA Guidelines to incorporate SB 743 requirements. The Office of Planning and Research (OPR) also issued a Technical Advisory on Evaluating Transportation Impacts in CEQA (2018), which recommends VMT as the preferred metric for transportation impact analysis. Key changes include eliminating LOS and similar congestion metrics as determinants of transportation impacts under CEQA.
The City of Temecula has adopted a VMT-based methodology for CEQA compliance. This includes defining VMT thresholds, establishing screening criteria, and identifying potential mitigation measures to address significant impacts. SB 743 emphasizes:
- Mitigating environmental impacts of traffic, including noise, air pollution, and safety.
- Balancing congestion management with broader goals like GHG reduction, infill development, and active transportation.
The VMT analysis framework enables projects to:
- Align with updated CEQA requirements.
- Identify significance thresholds and screening criteria for determining VMT impacts.
- Establish effective mitigation strategies to reduce VMT-related impacts below significance thresholds.
- Promote efficient use of transportation networks and alternative travel modes.
Vehicle Miles Traveled (VMT)
VMT measures the total distance traveled by vehicles, reflecting transportation network efficiency rather than traffic operations. It serves as a proxy for various environmental impacts, including energy consumption, air pollution, GHG emissions, safety risks, and roadway maintenance. VMT typically increases in areas with lower land-use density and greater reliance on automobile travel due to longer trip distances.
Metrics and Methodology for Calculating VMT
Definition and Calculation
VMT refers to the total distance a vehicle travels, regardless of the number of passengers. Basic calculations include multiplying average daily traffic (ADT) by roadway segment length or summing trip distances. Comprehensive analysis may require aggregating roadway or population group data.
Transportation Models
The Riverside County Transportation Analysis Model (RIVTAM) is recommended for CEQA VMT analysis. Outputs may include:
- VMT per Service Population: Total VMT divided by the sum of the population and employment.
- Total VMT: Aggregate VMT within a defined boundary, incorporating all trip types (internal and external).
VMT per Service Population Formula
VMT/Service Population=Total VMTPopulation + Employment\text{VMT/Service Population} = \frac{\text{Total VMT}}{\text{Population + Employment}}VMT/Service Population=Population + EmploymentTotal VMT
This metric reflects land-use accessibility and efficiency, with lower values in areas of higher density and mixed land use.
Boundary Method for Total VMT
This approach multiplies roadway segment length by daily traffic volumes within a specific boundary, such as the City of Temecula or a project vicinity.
Trip Length Adjustments
External trips leaving the RIVTAM area require adjustments using the California Statewide Travel Demand Model (CSTDM). Adjustments ensure accurate representation of trip lengths beyond model boundaries. Steps include:
- Identifying gateway zones.
- Calculating average external distances using CSTDM skims.
- Integrating weighted distances into the RIVTAM model.
Land Use Projects VMT Analysis
Projects are assessed based on their VMT/Service Population relative to regional thresholds. Any project generating VMT at least 15% below the baseline regional average is presumed to have a less-than-significant impact.
Screening Criteria
Certain projects may bypass detailed analysis if they meet criteria indicating inherently low VMT impacts, such as:
- Generating fewer than 110 daily trips.
- Proximity to major transit stops or high-quality transit corridors.
- Location in a VMT-efficient area (15% below baseline).
- Local-serving retail (<50,000 square feet).
- Affordable housing developments.
- Redevelopment projects with improved VMT efficiency.
Detailed Analysis
If not screened, projects must use RIVTAM to evaluate VMT impacts. Transportation Demand Management (TDM) measures can be applied to reduce project VMT. TDM reductions are calculated based on resources like the California Air Pollution Control Officers Association’s Quantifying Greenhouse Gas Mitigation Measures (2010).
Transportation Projects VMT Analysis
Screening Criteria
Projects that do not add motor vehicle capacity, such as road maintenance or bicycle infrastructure, are generally exempt from detailed VMT analysis.
Thresholds and Procedures
Projects increasing motor vehicle capacity may induce travel, contributing to higher area-wide VMT. Analysis requires:
- Inputting the project into a travel demand model.
- Comparing total boundary-method VMT with and without the project.
For freeway projects, Caltrans’ Transportation Analysis Framework or the NCST Induced Travel Calculator may be used to assess induced travel effects.
The City of Temecula’s VMT-based guidelines provide a robust framework for CEQA compliance. By shifting focus to driving impacts, these guidelines promote alignment with state sustainability goals while ensuring comprehensive environmental review and mitigation for land use and transportation projects.
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