ARB Research Seminar

This page updated May 9, 2016

Effects of Complete Streets on Travel Behavior and Exposure to Vehicular Emissions

Photo of Yifang Zhu, Ph.D.

Yifang Zhu, Ph.D., Associate Professor, Environmental Health Sciences Department, UCLA Fielding School of Public Health, University of California, Los Angeles

May 24, 2016
Cal EPA Headquarters, 1001 "I" Street, Sacramento, CA

Research Project


With growing interests in travel demand management, smart growth, climate change mitigation, and transportation safety and equity, increasing number of communities have adopted policies to promote complete streets. Complete streets are structured to make streets accessible for all users - drivers, transit users, pedestrians, cyclists, seniors, children, and people with disabilities. They are designed to encourage travel behavior changes to promote health benefits. However, there is little evidence of whether or how these changes take place with complete street conversion. In this study, we compared complete streets to incomplete streets to investigate their impact on travel behavior and street users' exposure to traffic-related air pollutants.

We employed two empirical study designs: a natural experimental design using before-after comparisons and a quasi-experimental design using a spatial difference-in-difference (DID) approach. In the before-after study, we investigated the volume of motorized vehicles, cyclists, and pedestrians as well as exposures to fine (PM₂.₅) and ultrafine particles (UFP) among drivers, cyclists, and pedestrians before and after two complete street retrofit projects. We also conducted a neighborhood survey in an area adjacent to one of the study sites before and after the retrofit. In the DID study, we selected six pairs of streets to represent a diversity of road types and land use contexts. Each pair was comprised of one complete street and one parallel incomplete street. We measured PM₂.₅ and UFP concentrations as well as traffic, pedestrian, and cyclist volume on each pair of streets to investigate the difference between complete and incomplete streets in exposure and travel behavior. We also conducted road-side intercept surveys at these six sites to assess street users' perceptions of the streets. Results from the before-after study showed that the emission-weighted traffic volume decreased 26% at one of the study sites, but it is unclear whether the decrease was caused by natural fleet turnover or by the complete street retrofit (or both).

The neighborhood survey results showed that the complete street retrofit project resulted in an increase of recreational biking and some increase in biking and walking to access public transit. The DID study results showed that for three out of the six pairs, the complete streets had significantly lower UFP concentrations than the incomplete streets, while all six pairs showed similar PM₂.₅ concentrations. Three out of six sites had lower total traffic volume on the complete streets compared with the incomplete streets, while two other sites showed just the opposite, and one site showed no significant difference.

The road-side intercept survey at the six sites showed that the street users believed that compared to the incomplete street, the complete street: (1) had more shade; (2) had more interesting things to do; (3) was more secure to walk on; and (4) was easier to cross. However, the retail establishments on the streets are also likely to affect the pedestrian and cyclist volume, as was found at one of the study sites.

Overall, the findings of this study, although preliminary and difficult to generalize, suggest that the complete streets have favorably impacted some, but not all, tested parameters and the differences between complete and incomplete streets are site-specific and vary greatly depending on the location and function of the complete streets.

Speaker Biography

Yifang Zhu, Ph.D., is an Associate Professor of the Environmental Health Sciences Department in UCLA Fielding school of Public Health, University of California, Los Angeles (UCLA). Dr. Zhu's research interest is primarily in the field of air pollution, exposure assessment, and aerosol research. Specifically, she is interested in quantitative exposure/risk assessments on ultrafine particles that have shown higher toxicity than larger particles on a unit mass basis. Dr. Zhu has published more than 70 peer-reviewed journal articles and book chapters, and received several national and international awards including UCLA Chancellor Scholarship, the National Science Foundation (NSF)'s Faculty Early Career Development (CAREER) Award, the Walter Rosenblith New Investigator Award from the Health Effects Institute, and the 2011 Haagen-Smit Prize from Atmosphere Environment in recognition of her outstanding publication on ultrafine particles near major freeways. Dr. Zhu was appointed to California Air Resource Board's (CARB) Research Screening Committee in January 2014. She received her B.Eng. in Environmental Engineering from Tsinghua University in 1997 and her Ph.D. in Environmental Health Sciences from UCLA in 2003.

For a complete listing of the ARB Research Seminars and the related documentation
for the seminars please view the Main Seminars web page