I will also note the Caltrans HQ (not the local Caltrans district doing the project) has just recently implicitly acknowledged three decades of understating the impact of the wider freeway on VMT and GHG in its CEQA guidance specifically:

• 30-year program of installing HOV lanes to reduce congestion and improve air quality were mismodeled. The billions spent here did not address air quality concerns by reducing travel or reducing congestion, i.e. they do not cause people to car pool more.
  
  
• The Caltrans new innovation “Managed Lanes” (aka Express lanes/variable toll pricing/HOV) are not “environmentally sustainable” as they do not overcome the GHG impact of regular freeway lanes.

Beware of GEEKs bearing gifts: Caltrans gets “free money” from feds & state gas taxes, so it is not unreasonable to believe that motivated reasoning is at play. There is a history of bias in the environmental analysis of these projects to justify using funds to build even wider freeways instead of funding local transit agencies. This tendency was shown in the Caltrans 2022 study of increasing mobility in the I-80 corridor: upgrading the Capitol Corridor rail was studied as an alternative, found more cost-effective, then ignored in it conclusions without explanation (see end notes for link to primary sources on this).[vi]

References/end notes: My comment on Caltrans are harsh, so It important to see they are backed up by links to these primary sources:

[i] The question about if a mitigation is valid is about if it is a truely an “additive” change, Will Caltrans VMT mitigation offset fund truely new “additive” projects beyond what is already planned and counted in a city’s CAP/CAAP or just double count what is already planned?.  For example, the West Sacramento CAP GHG reduction Plan already calls for an ambitious 40% reduction in car travel. Any mitigation paid for by Caltrans funding increase transit/micro transit and car-free housing should be on top of this 40%—if not  the Caltrans VMT mitigation will be double counted and not be true mitigation. Any city that accepts Caltrans mitigation funds will be faced with same problem. This type of mitigation plan (VMT banking) is untested in court. See John Oliver’s tongue and cheek critique on how similar Carbon Offset plans are gamed. https://youtu.be/6p8zAbFKpW0

 [1 Core of this article based on this carefully phrased, peer review piece::  Volker, Jamey et al:  Environmental Reviews Fail to Accurately Analyze Induced Vehicle Travel from Highway Expansion Projects https://escholarship.org/uc/item/14b0x0nm

 [ii] Volker, Jamey et al:  Environmental Reviews Fail to Accurately Analyze Induced Vehicle Travel from Highway Expansion Projects https://escholarship.org/uc/item/14b0x0nm

[iii] Citizens for a Better Environment vs Deukmejian, et al. This case put to a conclusive test Caltrans argument that wider freeways reduce congestion and air quality. Conclusive scientific evidence was present from decades of experience that when you widen a freeway, more traffic is generated to fill it. This article in Wired magazine discussed in more depth and gives real world examples of when freeways are removed traffic evaporates: What's Up With That: Building Bigger Roads Actually Makes Traffic Worse. The City of Davis succesfully tested this on 5^th Street with its “road diet,” that cut lanes from 2 to 1 on section of road. This was a change the Davis Public Works Department resisted for a decade.

[iv] SB743 impact on EIR and need to reduce VMT is discussed in “Rethinking How We Build So Californians Can Drive Less”  https://dot.ca.gov/programs/sustainability/sb-743  

[v]  Decades of research proving Induced Demand from wider freeways is cited by Professor Susan Handy, Director of the National Center for Sustainable Transportation, in recent article: Increasing Highway Capacity Unlikely to Relieve Traffic Congestion  https://escholarship.org/uc/item/58x8436d. EPA published this 16 page “Induced Travel Demand Literature Review” 20 years ago. Inconvenient truths are hard to institutionalize.

[vi] Rail alternative for I-80 ignored. Caltrans District 3&4’s. “I-80 Comprehensive Multimodal Corridor Plan (I-80 CMCP). Draft of 1/22 See Page 77 table 5.13 Benefit cost ratios for different alternatives by segment (segment 6 is Davis/Causeway). The rail alternative to improve I-80 mobility includes upgrades like 110 MPH trains, ½ hour service and a high bridge over Sacramento River so trains are not stopped by river traffic, pg. 60. Rail ridership would triple, pg. 66. This Inconvenient truth was not  publicized: The I-80 CMCP is not found on public Caltrans site for this project and has never been shared with Yolo elected–it is only found on a Solano County website. https://sta.ca.gov/wp-content/uploads/2022/01/Draft-I-80-CMCP.pdf   Of note, Caltrans claim in CMCP document that Yolo Transit District was in the  plan’s preparation but a public record request of Yolo TD turned up no such input or even a  request for input . I don’t expect Yolo TD to publicly acknowledge an issue here as Caltrans the purse strings.