VMT Impact Analysis
Projects that do not meet at least one of the screening criteria outlined in Section 2.0 must conduct a more detailed analysis and propose mitigation measures to address potential VMT impacts.
3.1 VMT Thresholds of Significance
According to Section 21099 of the Public Resources Code, the criteria for determining the significance of transportation impacts must promote: (1) reduction of greenhouse gas emissions; (2) development of multimodal transportation networks; and (3) a diversity of land uses.
The City of Laguna Hills has established the following thresholds of significance for VMT, based on recommendations from OPR and data from the Orange County Transportation Authority (OCTA):
- Residential Projects: A project is considered to have a significant transportation impact if its home-based VMT per capita exceeds the base year citywide average VMT per capita.
- Non-Residential Projects: A project is considered to have a significant transportation impact if its employment VMT per employee exceeds the base year citywide average VMT per employee.
These thresholds are determined using base year OCTAM modeling statistics. Ensuring that land use development projects have VMT rates at or below the citywide average will help to reduce overall VMT and greenhouse gas emissions.
3.2 Mitigating Impacts Using the VMT Screening Form
To streamline the VMT evaluation process, the City of Laguna Hills allows certain projects to use the base year VMT statistics from the OCTAM for the Traffic Analysis Zone (TAZ) where the project is located to mitigate potentially significant impacts.
Projects may use the VMT Screening Form for mitigation if they generate less than 2,400 ADT and are situated in a TAZ with sufficient demographic data to reasonably estimate VMT patterns. For example, residential projects must be in a TAZ with existing housing, and non-residential projects must be in a TAZ with existing employment to provide a valid sample size for evaluating and mitigating VMT.
Using base year VMT statistics from OCTAM is effective because similar land uses within the same geographic area tend to have similar access to transportation networks, producing and attracting trips in a comparable manner. This approach is consistent with the OPR Technical Advisory's map-based screening methodology.
A project must reduce the base year VMT rate for its TAZ to be less than or equal to the citywide VMT average. The percentage reduction required to meet the citywide average VMT is calculated accordingly.
3.3 Project-Specific VMT Modeling
Projects that do not meet at least one of the VMT screening criteria, generate 2,400 or more net daily trips, or cannot effectively mitigate impacts using the VMT Screening Form, must analyze VMT impacts using the OCTAM model for project-specific VMT.
The Orange County Congestion Management Program uses a threshold of 2,400 ADT to determine if a project may require a CMP-level Traffic Impact Analysis. Projects generating more than 2,400 ADT have a higher potential to affect travel demand patterns, thus necessitating a project-specific VMT analysis.
Project-specific VMT modeling should assess impacts under the following scenarios:
- OCTAM base year plus project conditions
- OCTAM future year with project conditions
VMT modeling must calculate the project's VMT per capita and/or VMT per employee and compare the results to the established significance thresholds.
The analysis must align with OCTAM zone boundaries, and new zones or adjustments to existing Orange County Projections (OCP) data and zone boundaries may be necessary. The latest version of OCTAM should be used.
Before commencing modeling, the traffic engineer must meet with city staff to determine the scope of analysis. This ensures that the modeling effort aligns with the guidelines.
3.4 RTP/SCS Consistency Requirements
CEQA Guidelines Section 15125(d) recommends analyzing impacts resulting from inconsistencies with regional plans, including Regional Transportation Plans (RTP) and Sustainable Communities Strategies (SCS). If a project is inconsistent with the RTP/SCS, the lead agency should evaluate whether that inconsistency indicates a significant impact on transportation.
For instance, a project may be inconsistent with the RTP/SCS if it is outside the development footprint or within a designated open space area. Additionally, if a project exceeds the number of housing units allocated in SCAG's Regional Housing Needs Assessment (RHNA) Final Allocation Plan, further modeling may be necessary to analyze the effect on future VMT rates.
3.5 Impacts to Transit and Active Transportation
Consistent with the OPR Technical Advisory, the City of Laguna Hills recommends that transportation impact analyses consider potential effects on transit systems and bicycle and pedestrian networks. For example, a project that blocks access to a transit stop or interferes with a transit route could negatively impact transit functionality.
The analysis should determine whether the project aligns with adopted policies, plans, or programs for active transportation or public transit facilities. It should also assess whether the project could decrease the performance or safety of these facilities or conflict with existing or planned infrastructure supporting these modes of travel.
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