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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 2023

The TRANSIT Accountability Study: Assessing the Effect of Decreased Tailpipe Emissions on Adverse Birth Outcomes over a 20-Year Period in Texas

Perry Hystad1, Elaine L. Hill2, Mary D. Willis1, Andrew Larkin1, David Schrank3, Max Harleman2, Evan Volkin2, John Molitor1, 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. However, few health studies have empirically evaluated the direct impact of TRAP reductions on infant health outcomes. We hypothesize that the magnitude of association between adverse birth outcomes and indicators of TRAP exposure would decrease over time, paralleling regulatory improvements in tailpipe emissions.   

Methods: We are implementing the Traffic Regulations And Neonates Study In Texas (TRANSIT) Accountability Study. For this specific analysis, we examined vital statistics data (n=7.2 million births) in Texas from 1996 to 2016. We linked several measures of TRAP to maternal residences at delivery, including distance to the nearest highway or expressway, the amount of annual vehicle miles traveled (VMT, a measure of traffic volume) within 500 meters, and nitrogen dioxide (NO2) concentrations from a spatial-temporal model. We implemented linear regression models to examine associations between each TRAP exposure measure and term birth weight, term low birth weight (<2,500 g), preterm birth (<37 weeks), and very preterm birth (<32 weeks) for annual 3-year rolling averages from 1996-2016 and examined interaction terms between TRAP exposure measures and time.

Results: Exposure to TRAP was consistently associated with negative birth outcomes over the 20-year period; however, the results were mixed on whether associations between TRAP exposures and birth outcomes became weaker over time. Interaction terms between TRAP measures and year were statistically significant and indicated small reductions in the odds of preterm and very preterm birth from TRAP exposure over time. No consistent trends were observed for term birth weight or low birth weight. The strongest decreases were for vehicle miles travelled (VMT) within 500m of addresses and very preterm birth (e.g. odds ratios for >20,000 VMT compared to <1500 were 1.15 (95% CI: 0.97, 1.37) in 1996-1998 compared to 1.08 (95% CI: 0.96, 1.20) in 2014-2016). Similar results were observed for truck VMT and for different buffer distances. The impact of a 1-unit increase in NO2 concentrations on birth outcomes were consistent across the 20-year period.  

Conclusions: We observed some evidence of improvements in birth outcomes associated with reductions in tailpipe emissions over a 20-year period in Texas; however, results varied by TRAP exposure metric and adverse birth outcome measure, and reductions in associations were much smaller than the 70% decrease in NO2 levels observed over this period.