Mitigation location: How far is too far?

June 5, 2024

Mitigating for transportation impacts under CEQA, as measured by vehicle-miles traveled (VMT), always involves some consideration of location. Whether the mitigation measure is a transportation demand management program, new transit service, additional housing, or anything else, there is always a question about where the measure should be located.

Determining the location for mitigation is not unique to transportation impacts under CEQA. Various resources require a determination of where suitable mitigation could occur. For example, mitigation for biological resources is generally most suitable in areas that are within the same watershed or habitat area as where the project impacts occurred. This ensures that habitats and species affected receive the benefits of the mitigation. Although some environmental effects that are related to VMT – e.g. greenhouse gas emissions – could extend broadly, others are more localized, so mitigation for transportation impacts should first seek first to identify locations as close as possible to the project corridor.

That does not mean mitigation has to be strictly limited to the project corridor. Induced traffic spreads like water and is not limited to new or widened segments, or abutting areas. For Interstates, we consider the whole metropolitan area in calculating VMT; for other freeways and arterials, we consider the county. So locating mitigation in the metro area or county is a good rule of thumb.

But there could be exceptions. For example, a project may be near the border of a metro area or county, so mitigation in the abutting area or county may be justified. Another possibility is that the mitigation measure may extend beyond the borders of the metro or county; for example, a widened Interstate may be  mitigated by additional parallel rail service that extends beyond the highway project limits into another county or metro area.

On the other hand, metro or county boundaries might also be too broad. While induced travel does spread, there may be disproportionate impacts at or near the project site or at some known up- or downstream location. If so, we should work to ensure that mitigation will provide benefits in those areas. This consideration is doubly important when increased traffic will occur in Priority Populations, as defined by the Caltrans Equity Index, CalEnviroScreen, or other tools. We do not want to create transportation impacts in Priority Population areas and mitigate them elsewhere, even within the same metro or county.

So the question of how close to a project a mitigation measure should be does not have a one-size-fits-all answer. Usually, but not always, mitigation should be in the same metro (Interstates) or county (other facilities). But beyond that, it should consider known localized impacts, particularly in Priority Population areas, and be able to show benefits in those areas.