High Traffic Roads and Adverse Birth Outcomes: Comparing Births Upwind and Downwind of the Same Road
This study provides robust evidence linking traffic air pollution to adverse birth outcomes, demonstrates clear distance-decay and demographic patterns in these effects, and introduces a novel methodological approach that could be valuable for future environmental epidemiology research. The findings have important implications for urban planning, environmental justice, and policies aimed at reducing traffic pollution impacts.
College of Health researcher(s)
Highlights
Living downwind of high-traffic roads was associated with an 11.6 gram decrease in term birth weight compared to living upwind of the same road.
The negative impact was larger for residences closer to roads. Within 50m of a major road, living downwind was associated with a 36.3 gram decrease in term birth weight.
Larger negative associations were observed for Black non-Hispanic births and those with lower education levels.
The study used wind direction as an instrumental variable to compare upwind vs downwind residences, helping to control for confounding factors.
The findings support efforts to reduce traffic-related air pollution, especially near residential areas.
Abstract
Traffic related air pollution is a major concern for perinatal health. Determining causal associations, however, is difficult since high-traffic areas tend to correspond with lower socioeconomic neighborhoods and other environmental exposures. To overcome confounding, we compared pregnant individuals living downwind and upwind of the same high-traffic road. We leveraged vital statistics data for Texas from 2007-2016 (n=3,570,272 births) and computed hourly wind estimates for residential addresses within 500 m of high-traffic roads (i.e., annual average daily traffic greater than 25,000) (10.9% of births). We matched pregnant individuals predominantly upwind to pregnant neighbors downwind of the same road segment (n=37,631 pairs). Living downwind was associated with an 11.6 gram (95% CI: -18.01, -5.21) decrease in term birth weight. No associations were observed with low term birth weight, preterm birth, or very preterm birth. In distance-stratified models, living downwind within 50 m was associated with a -36.3 gram (95% CI: -67.74, -4.93) decrease in term birth weight and living 51-100m downwind was associated with an odds ratio of 3.68 (95% CI: 1.71, 7.90) for very preterm birth. These results suggest traffic air pollution is associated with adverse birth outcomes, with steep distance decay gradients around major roads.
Traffic-Related Air Pollution and Birth Outcomes: FAQs
What is the main focus of this study?
This study investigates the causal relationship between traffic-related air pollution (TRAP) and adverse birth outcomes, specifically focusing on the impact of wind direction on exposure levels. The researchers aimed to overcome the challenge of confounding factors associated with living near high-traffic areas by comparing birth outcomes of pregnant individuals residing downwind and upwind of the same major roads.
How did the researchers assess TRAP exposure?
The study utilized hourly wind data and geographic information systems (GIS) to estimate the percentage of time each pregnant individual's residence was downwind of high-traffic roads within 500 meters. They calculated the mean hours and percentage of each pregnancy spent downwind, identifying the specific road segment contributing the most upwind hours. Building and tree shielding were also considered in the analysis.
What were the key findings of the study?
The primary finding was a significant association between living downwind of high-traffic roads and a decrease in term birth weight (TBW). On average, infants born to mothers residing downwind had an 11.6g lower TBW compared to those living upwind. This association was stronger for residences located within 100-300 meters of the road. No statistically significant associations were found for low TBW, preterm birth, or very preterm birth when considering all distances. However, when stratified by distance, residing downwind within 50 meters was associated with a 36.3g decrease in TBW. Additionally, living downwind between 51-100 meters was associated with a 3.68 times higher odds of very preterm birth.
How did the researchers address potential confounding factors?
The study employed a novel approach using wind direction as an instrumental variable. This technique allowed for a comparison of individuals exposed to differing levels of TRAP while residing in similar socioeconomic and environmental contexts. By matching pregnant individuals living upwind and downwind of the same road segment, the researchers minimized the influence of confounding variables typically associated with proximity to traffic.
Were there any differences in birth outcomes based on sociodemographic factors?
Stratified analyses revealed potential variations in associations based on certain sociodemographic characteristics. Notably, Black non-Hispanic individuals living downwind showed increased odds of preterm and very preterm birth. Individuals with lower education levels also exhibited a greater decrease in TBW when residing downwind.
What are the limitations of this study?
The study acknowledges several limitations:
- Wind data represented regional patterns rather than localized wind behavior, potentially leading to some exposure misclassification, especially within 50 meters of the road.
- Assuming the residential address at birth was the primary exposure location may not account for individuals moving or working elsewhere during pregnancy.
- The study design limited the number of matches within 50 meters of high-traffic roads, potentially underestimating effects in close proximity to roadways.
What are the implications of these findings?
The study's findings provide further evidence for a causal link between TRAP exposure and adverse birth outcomes. These results highlight the importance of considering wind patterns in assessing TRAP exposure and emphasize the potential health risks associated with residing near high-traffic areas, particularly for vulnerable populations.
What are the future research directions?
Future research should explore the use of higher resolution wind data and investigate the long-term health impacts of TRAP exposure. Further exploration of sociodemographic disparities in birth outcomes related to TRAP is also warranted.