California Air Resources Board

Principal Investigator/Author(s): Susan Handy

Contractor: University of California, Davis

Contract Number: 20STC008

Project Status: Completed March 2024

Relevant CARB Programs: Advanced Clean Fleets, Sustainable Communities & Climate Protection

Topic Areas: Climate Change, Sustainable Communities, Research, Transit, Zero-Emission Transportation

Research Summary:

This project developed four future scenarios that aim to capture differing post-COVID travel possibilities: COVID trends persist, return to pre-COVID trends, urbanism returns, and urbanism bounces ahead. These scenarios are defined by assumptions about five key modalities: telecommuting, e-shopping, ride-hailing, public transit, and active travel. The assumptions are based on an extensive review of the literature on pre-COVID trends, during-COVID changes, and post-COVID forecasts for each of these modalities.

To model these scenarios, the contractor used outputs from the California Statewide Travel Demand Model (CSTDM) for 2030 and 2050 and applied a post-processing approach that adjusted these outputs to reflect the specific assumptions of each scenario with respect to the five modalities. For each scenario, the contractor started with the CSTDM baseline projections at the Traffic Analysis Zone (TAZ) level for 2030 and 2050, which were developed before the COVID pandemic. They call this a business-as-usual (BAU) scenario. The post-processing uses the trip tables produced by the CSTDM and adjusts trips by mode and trip purpose according to the assumptions for the scenario. They examine numbers of trips, vehicle miles of travel (VMT), and mode shares for each scenario as a way to assess their implications for sustainability. In particular, more VMT and a higher share of travel by automobile, both of which contribute to greenhouse gas (GHG) emissions and other environmental impacts, are assumed to be an undesirable outcome from the standpoint of sustainability. 

The contractor also analyzed the equity implications of each of the scenarios. They compare the travel outcomes of VMT, trip length, and mode share aggregated by three socioeconomic characteristics: neighborhood designation using equity priority area definitions at the traffic analysis zone level, and household income and household car ownership at the trip level.  They also examine outputs by region where appropriate to understand the spatial distribution of transportation equity considerations. Although higher numbers of vehicle trips and VMT can reflect a positive outcome for some disadvantaged households (e.g. if the additional driving helps low-income workers reach higher paying jobs), they assume that more driving is generally a burden for disadvantaged households because: 1. Driving imposes a financial burden on these households, 2. It may reflect poor accessibility to jobs and other activities by more affordable modes, 3. The environmental impacts of driving are especially acute in disadvantaged communities.

The contractor explores a variety of policies the state could consider as a way to minimize the negative impacts while maximizing the positive impacts of post-COVID trends from the standpoint of both reducing GHG emissions and enhancing transportation equity.

A key finding is that trips and VMT increase compared to the pre-COVID forecast across the first three scenarios, though results differ with respect to patterns of mode use and trip purpose. The fourth scenario, which assumes the strongest shift toward alternatives to driving, results in a small decrease in VMT relative to the pre-COVID forecast. 

Results from the scenario analysis show that disadvantaged groups would continue to face burdens under some model assumptions. While the model predicts that disadvantaged groups (by geography, income, and car ownership status) will drive less and for shorter cumulative distance than advantaged groups in all scenarios, their driving is highest in the scenario where COVID-19 pandemic trends persist into the future, suggesting a high degree of burden compared to other scenarios. 

It is unclear which of the four scenarios the post-COVID future in California will most closely resemble. It is also possible that the future will reflect a combination of the scenarios – or will look very different than both the CSTDM and the assumptions in these scenarios suggest. Although these scenarios are hypothetical, the results provide useful insights into future travel patterns as well as a baseline against which to compare other possible post-COVID scenarios. The estimates of increases in VMT and total trips for three of the four scenarios is discouraging from the standpoint of meeting California’s goals for emissions reductions, but the differences between scenarios point to the importance of state, regional, and local policy in the state’s efforts.

Keywords: Vehicle Miles Traveled; greenhouse gas; telework; smart growth; freight; transit; active transportation; transportation equity