California Air Resources Board

Principal Investigator/Author: Dan Chatman

Contractor: University of California, Berkeley

Sub-contractors: University of Southern California, Occidental College

Contract Number: 22STC009

Project Status: Active

Relevant CARB Programs: Affordable Housing and Sustainable Communities

Topic Areas: Sustainable Communities, Sustainable Community Strategies (SCS), Climate Change, Vehicle Miles Traveled Reduction & Climate Goals, California Climate Investments, Building Decarbonization

Research Summary:

The Affordable Housing and Sustainable Communities (AHSC) program provides funding for affordable housing projects that are scored partly based on their expected contribution to reducing greenhouse gas emissions (GHGs). CARB has developed methods to estimate vehicle miles travelled (VMT) and GHG reductions, which are also used in the program’s scoring system. These methods could be further refined to account for up-to-date and empirically verified information on how housing project characteristics and surrounding land uses and services contribute to passenger vehicle use. This proposed project’s objectives are to evaluate CARB’s methodology in GHG emission reduction quantification and to suggest recommendations, if necessary. This proposal outlines detailed tasks and methods, relying partly on new types of data not used in previous studies, to validate and improve estimates of reduced VMT associated with AHSC projects. These include: (1) An evaluation of pre- and post-project activity levels with control groups consisting of non-AHSC affordable housing projects and market rate projects, using regression discontinuity and difference-in-difference methods with mobile-phone-based activity data, to enable better estimates of the impacts of placing projects in “low-VMT” versus “high-VMT” areas; (2) a more detailed exploration of how distance to transit and other neighborhood- and community-level built environment factors such as destination accessibility may influence VMT, conducting regression analysis using data from the Nationwide Household Travel Survey; (3) an analysis of whether housing unit size reduces drive-alone auto commuting, which could occur if larger housing units in dense settlements near transit enable household travel economies of scale and vehicle sharing at the household level, conducting regression analysis using data from the American Housing Survey; and (4) an analysis of how senior housing compares to conventional housing in trip generation rates and/or drive-alone auto commuting. The analysis results are expected to benefit the state of California by both evaluating and suggesting updates to the GHG emission reduction quantification methodology for the state’s flagship affordable housing program.

Keywords: greenhous gas emissions strategies; affordable housing; land use; Vehicle Miles Traveled (VMT); disadvantaged communities; transit proximity; density; trip generation rates