4.2.1 Project VMT Impacts
A project is considered to have a significant impact if its VMT per person/employee is more than 4% above the existing VMT per person for the unincorporated County. This threshold was identified through a study by Fehr & Peers during the General Plan process, focusing on development in the County's growth areas. Using the CAPCOA guidelines, the study estimated that the maximum feasible VMT mitigation achievable through Transportation Demand Management (TDM) measures is just over 4% for both residential projects and commute trips. Setting this as the threshold provides a practical target for County development projects.
When a significant impact is identified, the project’s VMT per person/employee must be mitigated to 4% below the baseline VMT per person. Mitigation should include TDM measures analyzed using the VMT-reduction methodology in Chapter 7 of CAPCOA’s Quantifying Greenhouse Gas Mitigation Measures (August 2010) and approved by the Traffic Division and Land Use Services Department. Alternatively, the project description can be modified to reduce VMT.
4.2.2 Cumulative VMT Impacts
Cumulative impacts should be evaluated for consistency with the adopted RTP/SCS. If a project is included in the RTP/SCS, its cumulative impacts are considered less than significant. If a project is inconsistent with the RTP/SCS, the analysis should assess its effect on VMT and determine if the unincorporated Countywide VMT increases or decreases compared to the VMT generated by the RTP/SCS. A significant impact occurs if the project increases the regional VMT per person/employee compared to the RTP/SCS assumptions.
4.2.3 VMT Mitigation Measures
To mitigate VMT impacts, applicants can consider the following strategies:
- Revisiting project design features or land use to reduce project trips or trip lengths.
- Developing in a more efficient area.
- Implementing TDM measures to reduce trip lengths or the number of trips generated.
If a regional program to reduce VMT is available, a fair share payment towards that program is considered acceptable. The following TDM measures, identified as feasible during the threshold setting exercise, should be considered for County development. The CAPCOA guidelines should be followed to quantify the VMT reduction for each measure:
- LUT-6: Integrate affordable and below market rate housing (0.04% - 1.20%). The amount of affordable housing would be project-specific.
- LUT-9: Improve the design of development (3.0% - 21.3%).
- SDT-1: Provide pedestrian network improvements. Applicable for subdivisions connecting to other developments in growth areas identified in the Countywide Plan, unincorporated Valley region areas, or unincorporated spheres of influence.
- SDT-2: Provide traffic calming measures (0.25% - 1%). Applicable for subdivisions connecting to other developments in growth areas identified in the Countywide Plan, unincorporated Valley region areas, or unincorporated spheres of influence.
- TRT-4: Implement subsidized or discounted transit passes (0% - 16%). Applicable to developments within 1/2 mile of a transit system, primarily in the Valley region.
- TRT-6: Encourage telecommuting and alternative work schedules (0.2% - 4.5%). Applicable countywide, as the County partners with internet providers to increase coverage.
- TRT-10: Implement a school pool program (7.2% - 15.8% reduction in school VMT). Applicable for large developments of approximately 300 households or more.
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