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The TRANSIT Accountability Study: Assessing impacts of vehicle emission regulations and local congestion policies on birth outcomes associated with traffic air pollution

Principal Investigator: 

Oregon State University

This study will assess the effects of emission-control measures on birth outcomes associated with traffic-related air pollution in Texas. Hystad and colleagues will evaluate air quality changes associated with national motor vehicle emissions regulations, as well as a diverse array of local congestion reduction programs implemented in Texas over the past 25 years.

Funded under

Poster abstract for HEI Annual Conference 2022

Impacts of Vehicle Emission Regulations and Local Congestion Policies on Birth Outcomes Associated with Traffic Air Pollution: The TRANSIT Accountability Study

Perry Hystad1, Elaine L. Hill2, Mary D. Willis1, Andrew Larkin1, David Schrank3, Max Harleman2, Evan Volkin2, John Molitor1, Chunxue Xu1, Lena Harris2, Beate Ritz4  

1Oregon State University, Corvallis, OR, USA; 2University of Rochester; Rochester, New York, USA; 3Texas Transportation Institute, Bryan, Texas, USA; 4University of California, Los Angeles; Los Angeles, California, USA

Background: In the United States, billions of dollars have been spent implementing regulations to reduce traffic-related air pollution (TRAP) from tailpipe emissions. In addition, local programs have been implemented to reduce traffic congestion, for example, through road expansion or electronic tolls. Few health studies have empirically evaluated the direct impact of TRAP reductions from these emission regulations and congestion reduction programs, and no studies have examined infant health, which represent an important population health outcome that is strongly linked to air pollution exposures.  

Methods: We are implementing the Traffic Regulations And Neonates Study In Texas (TRANSIT) Accountability Study. We leverage a diverse population-based cohort of 7.6 million births in Texas from 1996-2016 and integrate novel datasets of connected vehicle data, property types, housing transactions, and GIS and satellite data to refine TRAP exposures and comprehensively examine confounders and effect modifiers. Our main hypotheses are: 1.) the magnitude of association between adverse birth outcomes and TRAP exposures will decrease over the 1996-2016 time period; and 2.) implementation of specific traffic reduction programs will be associated with decreased risks of adverse birth outcomes. These hypotheses will be tested via a research triangulation framework, integrating natural experiments, direct analyses of congestion, wind direction, and vehicle volume change.

Results: We observe steady decreases in NO2 exposures for pregnant women in Texas (14.7 ppb for 1996 compared to 6.4 ppb in 2016) but similar exposure to vehicle miles travelled (VMT) (VMT within 500m of addresses is 20,594 for 1996 and 20,700 for 2016). Leveraging connected vehicle data to measure vehicle congestion linked to 2015/16 births (n=580,992) we find consistent adverse associations between traffic congestion and term birth weight (e.g. -14.1 g (95% CI: -18.6, -9.6) for the highest quintile of delay in 300 m compared to low congestion). When we examine wind (a validated instrument for air quality), we observe a -17.1 g (95% CI: -25.8, -10.0) decrease in term birth weight for mothers who live predominantly downwind from roads with high vehicle volume (>25,000 annual average daily traffic) compared to upwind matched controls. In addition, we created a standardized construction project database for the entire state that comprises ~1,500 projects and includes detailed information on construction location, timing, cost, and type, as well as traffic volume and congestion measures and existing air quality measurements. We will then evaluate how different projects affect traffic and air pollution levels and examine impacts on birth outcomes using difference-in-differences analyses.

Conclusions: The TRANSIT Accountability Study will provide important new evidence on the impact of vehicle emission regulations and local congestion policies on infant health.