Does low birth weight cause congestion?

It’s not in your head. Traffic jams are really getting worse. According to a 2020 Report from the US Department of Transportation, the average person living in one of the 75 largest US cities in 1982 faced seven hours of travel delay per year. By 2001, this figure had jumped to 26 hours of lateness per year.

Traffic jams are more than just an annoying time drain. There could be negative health effects due to air pollution emitted by idling cars, with one study estimating that emissions from passenger vehicles a jump of up to 200 percent during peak hours which increases the concentration of air pollutants in areas around highways. It affects many people, with more than It is estimated that 11 million Americans live within 150 meters of freeways.

[Related: Why congestion pricing reduces traffic better than new highway lanes.]

“Traffic delays have steadily increased in the United States since the 1980s, but we know very little about the unique impact that traffic delays may have on population health,” said Mary Willis, a postdoctoral researcher in epidemiology at Boston University PopSci.

Willis is the lead author of a study published today in the Scientific progress which explores the role that congestion can play in a specific health scenario: birth weight. “Although there are many health outcomes we could study, low birth weight is particularly important because it can lead to immediate consequences, such as breathing problems, and long-term lifelong problems, such as cardiovascular disease, cognitive effects and premature death,” Willis said. For the first time, the team was able to make a link between congestion and pregnancy outcomes in nearby neighborhoods in the US

Willis and her colleagues examined the relationship between traffic congestion and outcomes of 579,122 births at addresses within 500 meters of road segments in Texas from 2015 to 2016. In this data, they found a strong association between traffic congestion and lower birth weights, with birth weight on average 9 grams lower in the highest quintile of exposure to traffic delays. The study notes that more research is needed to determine whether other socioeconomic influences (diet, income, access to prenatal care, etc.) not included in this study have any impact on this relationship between air pollution and adverse birth outcomes. These results show a link between air pollution and low birth weight, but not that pollution is the direct cause, as other forces may be at play.

“A 9-gram reduction in itself is not a clinically significant result, but this result suggests that some type of biological impact may be occurring that will push some infants toward a clinically relevant adverse impact,” Willis said. “When you multiply that by the 27 percent of all births in high-congestion areas, this small reduction in birth weight really translates into a significant potential impact at the population level, affecting up to 1.3 million babies a year.”

According to Willis, one of the surprising results of this study is an entirely new way to measure exposure that is separate from car tailpipe emissions. Instead, this metric focuses on the path delay process. “Traffic engineers and urban planners can analyze this data to understand where vehicle speeds are slower than expected, indicating congestion and delays. In our analysis, we used the aggregated connected vehicle and device data to examine ‘traffic delay,’ the total person-hours of delay on roads near mothers’ homes,” Willis explained.

[Related: Pollution kills 1 in 6 people worldwide.]

Exhaust emissions are largely regulated by the federal government. Solving congestion, however, depends on many more local policy changes. Although this study did not look at how to do this, some studies show that small steps such as installing sound barriers or plant barriers and updating zoning laws to prevent schools or daycares from being built near highways could help.

One solution that won’t help is building bigger highways. In an interview with PopSci in August Nicholas Klein, an assistant professor of urban and regional planning at Cornell University, said: “For many decades in the US, people have recklessly tried to solve this problem by adding more lanes,” he explains. “Not working due to induced demand. Every time you add capacity, it causes people to change their behavior. Klein says people will change their behavior by choosing to drive instead of using public transit if they see more available lanes.

Traffic exposure is also not evenly distributed. “We’re in the process of diving deeper into socioeconomic and racial disparities in exposure to congestion,” Willis said. “In particular, we are interested in considering how patterns of disparity may have changed over time as other processes such as urbanization and gentrification occur in metropolitan areas.”