A California court of appeal has held that a lead agency conducting environmental review, under the California Environmental Quality Act (CEQA), of “vehicle miles traveled” (VMT) impacts may not unquestioningly use thresholds for determining impact significance that borrowed from the recommendations of other agencies.
Notably, the court rejected San Diego County’s reliance on thresholds recommended by the state Office of Planning and Research (OPR), which promulgated the CEQA Guidelines provisions governing transportation impact analysis (i.e., Guidelines section 15064.3), and also prepared a Technical Advisory for agencies implementing CEQA’s VMT requirements.
Rather, the court held, each lead agency must determine, based on fact-based substantial evidence, that the VMT significance thresholds it elects to use – regardless of their origin – are suited to the purpose of identifying significant VMT impacts in the particular circumstances.
The case, Cleveland National Forest Foundation v. County of San Diego (2025), concerns a challenge to the County’s adoption of two thresholds for “screening” for general use (i.e., determining without further analysis) that certain types of projects will result in less-than-significant VMT impacts. The Petitioner challenged two such screening thresholds, namely the thresholds for: (1) “infill” projects proposed within the County’s unincorporated villages (the “Infill” threshold), and (2) projects expected to generate no more than 110 automobile trips per day, regardless of where they are built (the “Small Project” threshold).
The Court found that the County failed to support its Infill and Small Project thresholds because it did not show, based upon substantial evidence, that those thresholds were appropriate and useful to identify projects that in most cases would cause less-than-significant VMT impact, given the unique local conditions of the area under the County’s jurisdiction.
The opinion also cites advice in OPR’s Technical Advisory that “a per capita or per employee VMT that is 15% below that of existing development may be a reasonable threshold” for determining the significance of VMT impacts. While the Court observed that “OPR’s Technical Advisory does not indicate that its 15% standard must be satisfied for every project,” it also held that “because OPR wrote both the Technical Advisory and Guidelines section 15064.3…, the former is relevant to interpreting the latter.”
The Infill Threshold
The County adopted its Infill threshold based on language in Guidelines Section 15064.3, providing that a project located within one-half mile of a major transit stop should generally be presumed to have less-than-significant VMT impacts. To further support its Infill threshold, the County relied upon:
- OPR’s Technical Advisory to implement CEQA’s requirement generally to evaluate transportation impacts based on VMT, which concluded that “development in more dense areas with high job accessibility leads to more diversity in land use, demand for transit (bus and trolley) and multimodal infrastructure (walking and biking), and shorter vehicle trip, which reduce greenhouse gases and VMT,”
- the California Air Pollution Control Officers’ Association (CAPCOA) handbook, which observes that “VMT decreased with increased density,” and
- the County’s transportation study which concluded that “most locations within the County, even within suburban areas, tend to generate VMT at or about [rather than below] the regional mean.”
Nevertheless, the Court concluded that the County failed to demonstrate that “development consistent with the adopted infill threshold will normally or likely result in an insignificant impact.” The Court reasoned: (1) OPR’s Technical Advisory merely referenced infill development generally, but did not provide specific support for concluding all such projects to result in less than significant impacts, (2) CAPCOA’s advisory was inapplicable in infill locations, and (3) that the County’s transportation study “rather than showing that infill development as defined by the County will normally or generally result in transportation effects that are VMT insignificant, the evidence indicates the opposite.”
Small Project Threshold
The Court also invalidated the County’s Small Project threshold, holding that the County failed to demonstrate this threshold was appropriate to determine, without further analysis, that VMT impacts of all such projects would be less than significant. The County supported its threshold by citing OPR’s Technical Advisory, which advised that projects producing 110 trips or fewer per day “could be considered not to lead to a significant impact.” However, the Court rejected the County’s reliance on OPR’s recommendation, reasoning that the OPR’s small-project advice “was developed by evaluating projects across the State and was not developed based on a single jurisdiction.” Therefore, the court held that that the County did not properly adopt OPR’s recommended threshold without assessing, based on substantial evidence, whether it was appropriate and useful for application in the specific local or regional conditions pertaining to the project undergoing review by the County.
Key Takeaways
- Local agencies should not rely exclusively on OPR recommendations in adopting VMT screening thresholds, but should perform a local or regional-specific analysis of whether such projects would generally result in an insignificant transportation effect, even if they do not always do so.
- Agencies should avoid relying exclusively on generic, state-wide studies of similar projects to show the VMT impact in their jurisdiction would be less than significant.
- Rural and suburban agencies should be mindful that such analysis may show infill or small projects do not result in VMT decreases due to existing land uses that are less effective at VMT reduction than urban areas.
- Public agencies should specifically identify their underlying VMT reduction goals (e.g., at or below baseline, 15 percent reduction below baseline, developing multimodal transportation networks, or developing a diversity of land uses).
