CEQA Vehicle Miles Traveled (VMT) Impact Thresholds for the project in City of Diamond Bar

CEQA Vehicle Miles Traveled (VMT) Impact Thresholds

The California Environmental Quality Act (CEQA) has shifted its transportation impact evaluation framework from Level of Service (LOS) to Vehicle Miles Traveled (VMT), a metric that emphasizes reducing travel distances and promoting sustainable transportation. This change aligns with the state’s efforts to decrease greenhouse gas emissions and meet climate change goals, as well as other environmental benefits, by focusing on transportation efficiency. The VMT impact thresholds are designed to assess the effect of new development projects on vehicle travel behavior, specifically measuring how these projects might influence the total miles driven by residents, employees, and visitors.

The following sections detail the impact thresholds and mitigation measures used to assess and reduce VMT impacts under CEQA regulations. These guidelines apply to projects in the City of Diamond Bar, but the principles can be adapted to other regions implementing SB 743, which mandates the use of VMT in transportation analysis.

VMT Impact Thresholds

The assessment of VMT impacts is divided into two categories: project-generated VMT impacts and project effects on VMT.

1. Project-Generated VMT Impacts

A project is deemed to have a significant impact on VMT if it increases the VMT generated by the development beyond a certain threshold. Specifically, two conditions are considered for determining if a project-generated VMT impact is significant:

• Baseline VMT Per Service Population: The project-generated VMT is compared to a baseline established for the City of Diamond Bar. If the project's VMT per service population (residents and employees) exceeds 15% below the city’s baseline VMT per service population, it would be considered significant. This means that the project must demonstrate it generates fewer miles of vehicle travel per person compared to the city's average.

• Cumulative VMT Impact: Similarly, when considering the cumulative effect of the project in combination with other planned developments, if the project’s VMT per service population still exceeds 15% below the city’s baseline, the cumulative impact is also deemed significant. This cumulative assessment ensures that large-scale developments do not lead to unchecked increases in vehicle travel over time, even if individually they seem manageable.

2. Project’s Effect on Citywide VMT

In addition to examining the VMT generated by the project itself, the project's overall effect on citywide VMT must also be evaluated. A significant impact occurs if the project leads to an increase in Citywide VMT per service population under cumulative conditions compared to a scenario without the project. This assessment is typically conducted using a travel demand forecasting model that simulates how traffic patterns evolve with and without the project.

The key takeaway is that a project is likely to be considered impactful if it causes more driving than would occur under the existing or baseline conditions. For example, a large office building that attracts long-distance commuters or a new housing development far from job centers might significantly increase VMT if not properly mitigated.

VMT Mitigation Measures

When a development project is found to have a significant VMT impact, mitigation measures must be implemented to reduce the effect. There are three broad categories of strategies available to mitigate VMT:

1. Modify the Built Environment

One of the most effective ways to reduce VMT is by altering the physical characteristics of a project’s built environment. This could involve improving pedestrian, bicycle, or public transit access, promoting higher-density land use, or creating mixed-use developments that reduce the need for long vehicle trips. For example, designing a project that integrates residential, commercial, and office spaces can reduce the need for residents to drive long distances for work, shopping, or other services. Encouraging walkability and providing easy access to public transit options are essential components of reducing VMT in the built environment.

2. Implement Transportation Demand Management (TDM) Measures

Transportation Demand Management (TDM) strategies focus on reducing the need for driving by influencing travel behavior. These measures aim to reduce VMT by encouraging the use of alternative modes of transportation, staggering work hours, carpooling, telecommuting, or other programs that reduce reliance on single-occupancy vehicles. TDM programs are especially useful in employment centers or large residential developments, where policies can be enacted to promote alternative commuting options for residents or employees. A comprehensive TDM plan might include measures such as:

• Subsidizing transit passes for employees
• Providing bicycle parking and shower facilities for cyclists
• Offering ride-sharing programs
• Implementing remote work options
• Introducing flexible working hours to reduce peak-hour traffic congestion

The TDM plan should be supported by case studies or empirical data demonstrating the effectiveness of such measures in reducing VMT. In many cases, TDM measures alone may not be enough to fully mitigate the impacts, but they can contribute to significant reductions.

3. Participate in VMT Fee Programs or Mitigation Banking

Another strategy for reducing VMT impacts is through participation in a VMT fee program or VMT mitigation banking, if available. These programs allow developers to contribute to regional efforts to reduce VMT in exchange for the right to develop their projects. The idea is that some developments may have limited capacity to directly reduce VMT on-site, but through a regional program, they can help fund infrastructure improvements, transit projects, or other measures that reduce VMT elsewhere. VMT mitigation banking works similarly to carbon offset programs, where developers can invest in projects designed to reduce VMT on a broader scale.

VMT Reduction Strategies and Monitoring

A variety of strategies have been identified as effective in reducing VMT, and many of these are detailed in state guidelines or local transportation planning documents. Examples of common VMT reduction strategies include:

• Improving Transit Services: Increasing the frequency, reliability, and accessibility of public transportation reduces the need for private vehicle use.
• Land Use Mix: Encouraging mixed-use development where residential, commercial, and office spaces are within close proximity promotes walking, cycling, and shorter vehicle trips.
• Parking Management: Limiting parking availability can reduce the attractiveness of driving, especially in urban areas with good transit access.
• Incentives for Active Transportation: Providing incentives such as bike lanes, bike-sharing programs, and pedestrian-friendly infrastructure can encourage non-motorized transportation.

It is important to recognize that many of these strategies depend on the behavior of tenants and residents over time. Therefore, predicting the actual VMT reductions from TDM measures can be challenging. To address this uncertainty, projects using TDM measures for mitigation should be regularly monitored to ensure compliance and effectiveness. Ongoing data collection and analysis can help determine whether the VMT reductions anticipated in the project’s planning stages are being realized in practice.

Transportation Demand Management Plans (TDMs) as Mitigation

When a project is found to have a significant impact under CEQA, developers are required to implement Transportation Demand Management (TDM) plans. TDM plans are specifically designed to manage the demand for vehicular travel and to reduce peak-hour and overall vehicle trips generated by the project. As part of the project’s traffic study, the TDM plan must be thoroughly outlined, and it should include details on how the strategies will be implemented and maintained over time.

Key Components of a TDM Plan

A robust TDM plan will include the following components to ensure it is effective and enforceable:

1. Detailed Plan Description: The TDM plan should outline the specific measures that will be implemented to reduce vehicle trips. For example, it might include providing free public transit passes to residents or workers, setting up carpool matching programs, or offering bike-share memberships.

2. Supporting Data: The traffic study should include case studies or empirical data that support the projected traffic reductions attributed to the TDM plan. For instance, similar developments that implemented comparable measures can be used as benchmarks to estimate the potential effectiveness of the proposed plan.

3. Traffic Impact Calculations: The TDM plan must include updated Volume/Capacity ratio calculations to demonstrate how the proposed measures will alleviate congestion and reduce the project’s overall traffic impact.

4. Monitoring and Enforcement: A plan for monitoring the TDM measures over time must be included. This ensures that the TDM strategies remain effective and are properly enforced. Regular monitoring could involve tracking the number of transit passes distributed, surveying residents or employees about their commuting habits, or conducting periodic traffic counts.

5. Regulatory Compliance: The TDM plan must comply with relevant regulations, including those set by the South Coast Air Quality Management District (SCAQMD). This ensures that the plan not only reduces VMT but also contributes to broader efforts to improve air quality and reduce emissions.

Conclusion

As the City of Diamond Bar and other regions shift towards a VMT-based approach to transportation impact analysis under CEQA, developers must carefully evaluate their projects' potential effects on vehicle travel. VMT thresholds ensure that projects contributing to increased vehicle travel are properly mitigated, whether through modifying the built environment, implementing TDM measures, or participating in regional mitigation programs. The success of this approach depends not only on accurate assessments of VMT impacts but also on the long-term monitoring and enforcement of mitigation measures to ensure that the anticipated benefits are realized.

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