BOSTON — Around the United States, birthweights have steadily declined. Now, researchers from Boston University School of Public Health (BUSPH) suggest that this trend may have a connection to traffic congestion.
So far, there is mounting evidence that pollution coming from vehicles has an association with poor health, but there’s limited information about bottleneck traffic.
“For years, we’ve had detailed models to predict air pollution, but these models largely omit traffic congestion – because it could not be measured at a large scale,” says corresponding author Dr. Mary Willis, assistant professor of epidemiology at BUSPH, in a university release.
“If there are 10,000 vehicles on a road doing stop-and-go traffic, the air pollution concentrations, and likely composition, is very different compared to 10,000 vehicles at free-flow speeds. Our results show that there are likely health impacts specific to congestion, which are not included in most environmental risk assessments or cost-benefit analyses—and we think that those should start to be included in the conversation.”
Since 1982, traffic delays have risen continuously. As such, the researchers chose to investigate possible associations to low birthweight because it can lead to sudden and long-term health complications like difficulty breathing, cardiovascular disease, impaired cognition, and premature death.
Traffic can lower birthweight by 9 grams
This study is the first to examine the impact of congestion on birthweights, specifically due to traffic congestion in large metropolitan areas. To conduct their investigation, the team used data from almost 580,000 birth certificates in Texas and measured congestion levels through connected vehicles and devices that display driving volumes and traffic speed.
After controlling for background air pollution levels, transportation noise, and other environmental contaminants, the results showed that mothers who lived near highways were more impacted by traffic, with 260,000 pregnancies occurring in areas with lots of congestion. The results also showed that up to 1.3 million pregnant women, or 27 percent of all U.S. births, may be exposed to high levels of traffic congestion annually.
The pregnancies happening near these areas were found to result in newborns that weigh nine grams less than normal. This may not seem like much on its own, but the team says it’s significant in the bigger picture.
“A nine-gram decrease alone isn’t a clinically significant result on its own, but this result indicates that some sort of biological impacts may be happening, which will push some babies into a clinically relevant adverse impact of low birth weight,” Willis says. “When you multiply that by 27 percent of all births being in high-congestion areas, that small decrease in birthweight does translate into a substantial potential impact at the population level.”
These results can become part of the discussion about traffic and environmental policies that better support public health. Willis and the team are also planning to study racial and socioeconomic implications of urban living and the relationship to birthweight.
The findings are published in the journal Science Advances.