SB 743 at 10: The Environmental Effects of Traffic

SB 743, which changed the way California governments assess transportation impacts during environmental reviews, turns ten this year. Much progress has been made since the legislation was enacted, but much about SB 743 still seems new. On this 10-year anniversary, it is worth stepping back from the detailed implementation work to recall the motivation for both the law and the ongoing work to implement it.

In drafting SB 743, the legislature found that the old method for assessing transportation impacts, both for land use developments and transportation projects, was outdated and counterproductive, for example, in the way it burdened infill development. The bill stated that “Transportation analyses under the California Environmental Quality Act … typically study changes in automobile delay. New methodologies under the California Environmental Quality Act [CEQA] are needed for evaluating transportation impacts that are better able to promote the state’s goals of reducing greenhouse gas emissions and traffic-related air pollution, promoting the development of a multimodal transportation system, and providing clean, efficient access to destinations.”

Subsequent rulemaking and technical guidance from the Office of Planning and Research focused on a new methodology that accounts for vehicle miles traveled (VMT). Instead of considering auto speeds, as measured by the level of service (LOS) on roadways, transportation impacts would henceforth be assessed based on the amount of additional traffic, or VMT, that projects would induce. In shorthand, California moved from LOS to VMT in CEQA reviews. Following OPR, Caltrans’ policy and implementation guidance to this effect, focusing on the State Highway System, was published in 2020[1].

The motivation for all this work, and the ongoing efforts to apply the rules and guidelines, is closely linked to the state’s climate policy. And for good reason. The bill prominently cites “reduction of greenhouse gas emissions” as a goal, as do subsequent agency implementation materials. The rationale is straightforward: Transportation is by far the top-emitting sector for climate pollution in California, and the more traffic there is, the more emissions there are. VMT is a top target in the climate scoping plans prepared by the California Air Resource Board per AB 32 (2006) and in regional Sustainable Communities

Strategies per SB 375 (2008). However, as the 2022 scoping plan states, “We are not on track to achieve the VMT reduction called for in the 2017 Scoping Plan and will need to double down….” SB 743 reinforces the earlier plan-based approaches by addressing VMT from individual projects.

State climate action also extends to the related issues of vehicles and fuels, with phaseouts of many combustion engine vehicles planned. Yet it will be decades before combustion engine vehicles, including those still being built and sold, are retired. Zero-emission vehicles accounted for just under 3 percent of light-duty vehicles in California at the end of 2021, and the truck fleet has barely begun to convert. Even many decades from now, after vehicle conversion takes place, the climate pollution from roadway infrastructure will continue to make VMT a climate concern.

Yet climate is far from the whole story. VMT can have numerous adverse outcomes. SB 743 uses this term for the broad category of issues: “the environmental impacts of traffic.”

As noted, climate pollution is one such environmental impact, but the legislation’s findings and intent sections list many more:

• "Reducing … traffic-related air pollution": Motor vehicles emit criteria pollutants as well as greenhouse gases. Even ZEVs fueled with 100 percent clean energy continue to emit particulates from tire and brake wear. As with greenhouse gases, the more we drive, the more we emit other pollutants.
• "Promoting the development of a multimodal transportation system," and "Promotion of public health through active transportation": Higher VMT makes it harder for people to travel by walking, biking, and transit. The traffic itself and the infrastructure needed to accommodate it can make other modes less viable, e.g., adding additional wait times and travel distances for pedestrians, including those using transit, or adding to the “level of traffic stress,” which discourages active travel.
• "Providing clean, efficient access to destinations": Projects that induce VMT create new traffic and congestion – on the new facility itself, nearby roadways, or both. Maintenance costs rise, and the new traffic may spur additional widening, with new infrastructure, maintenance and environmental costs, and more induced traffic. This is far from clean or efficient, with mounting impacts on stormwater, heat islands, greenspace consumption, and personal and government budgets, among other policy topics.
• "Noise": Traffic noise is a function of traffic volume, speed, and other factors. And traffic noise is not just an aesthetic annoyance but a significant health concern, known, for example, to cause hypertension.
• "Safety": Here again, VMT is a driver. According to research cited in OPR’s General Plan guidance, "Multiple traffic safety studies showed that higher VMT was positively associated with the occurrence of traffic crashes or fatalities (e.g. Ewing et al. 2002, 2003; NHTSA 2011). The causal relationship between the mileage of total vehicle trips and crash occurrences can be explained by probability. With higher VMT, it is more likely that more crashes will occur (Jang et al. 2012).”
• "Infill development": As Caltrans’ Transportation Analysis Framework points out, induced travel happens partly because added roadway capacity (at least at first) facilitates longer trips and leads to more dispersed land use, leading to more VMT.

The legislation does not explicitly exhaust all the environmental effects of traffic, as it implies by introducing them as examples with the phrase “such as.” For example, OPR's Technical Advisory points out that "the natural environment is impacted as higher VMT leads to more collisions with wildlife and fragments habitat.” We also know that VMT is a significant environmental justice concern, as many lower-income and underserved communities are disproportionately affected by traffic. For this reason, Caltrans’ practice is to ensure that new highway capacity that induces traffic in a priority population area is mitigated to benefit the people in that area.

If we were to list all of the environmental effects of traffic, could we dispense with VMT and address those effects separately? Probably not. Even if we could enumerate every environmental impact of traffic, dealing with them separately would be like trying to address the public health effects of smokestack emissions one by one – it’s good to provide filters and treat kids with asthma. Still, it’s better to reduce the emissions in the first place. Thus, as with other pollutants, our goal is to reduce traffic, not simply try to accommodate it as we used to.[2]

In summary, ten years after the passage of SB 743, we focus on induced traffic as a climate imperative, but not only for that reason. As was envisioned in the legislation, we are addressing the environmental effects of traffic. We need to use abstract-sounding terms like VMT for technical reasons to have a metric to assess induced travel. But in plain language, our goal has been, and remains, very straightforward and non-technical – to allow Californians to meet their needs without requiring them to make longer and more motor vehicle trips and to avoid the impacts those longer and more frequent trips would cause.

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[1] From the 2020 policy memo: “Consistent with the language of Section 15064.3 of the CEQA Guidelines, Caltrans concurs that Vehicle Miles Traveled (VMT) is the most appropriate measure of transportation impacts under CEQA.”

[2] An issue that sometimes arises due to the close connection between VMT and climate relates to location. If VMT were solely a concern of greenhouse gas pollution, and we could show that a new highway project was moving VMT around, we could argue that the climate effect is neutral. That showing would be very difficult, but when we consider the environmental effects of traffic writ large – traffic as the pollutant – then such a showing is not enough. We must avoid imposing new traffic on communities] and mitigate it when we fail to prevent it. That is the case even if traffic is somehow reduced somewhere else.