Los Angeles County Traffic Study Guidelines Section 3.2.4.2. - Cumulative Impacts Determination
Analyses should account for both short-term and long-term effects of transportation projects on Vehicle Miles Traveled (VMT). Short-term impacts are assessed in the project-level VMT analysis outlined previously. Long-term cumulative effects are evaluated based on alignment with the SCAG RTP/SCS, a regional plan demonstrating adherence to air quality conformity standards and greenhouse gas (GHG) reduction targets. Projects integrated into this plan contribute to regional solutions for achieving air pollution and GHG reduction goals, thereby indicating a less than significant cumulative impact on VMT.
Transportation projects not conforming to the SCAG RTP/SCS could potentially exert a significant cumulative impact on VMT. Further scrutiny is required to ascertain whether such projects induce a noteworthy cumulative VMT impact. This analysis involves simulating the RTP/SCS cumulative year conditions alongside the cumulative “plus project” scenario (as detailed in the Los Angeles County Senate Bill (SB) 743 Implementation and CEQA Updates Report), incorporating network modifications resulting from the proposed transportation project. Any observed increase in VMT must be adjusted using an induced demand elasticity factor. A VMT increase beyond established thresholds would signify a significant impact, potentially compromising regional air quality conformity and GHG reduction efforts.
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