Background: Study Methods

Methods of School Bus Retrofitting Study

Figure 1: Methods of School Bus Retrofitting Study. 2,656 school buses in Georgia received new diesel engines, covering 150,000 students at an average cost of $8,110 per engine. Researchers compared the academic and physical performance of kids in school districts in Georgia that received retrofitted school bus engines with other nearby schools that did not.

School buses are a great American institution. Around the country, they make sure that kids can get to school safely and on time regardless of socioeconomic status.

But, they can have a serious pollution problem. Typically, these buses run on diesel. Modern diesel engines can be exceptionally clean. However, many cash strapped school districts use buses that are decades old and outdated.

Now, new evidence is showing that low air quality inside older school buses may affect kids' learning and physical health.

Researchers in Georgia found opportunity to study this when federal funding allowed certain school districts to retrofit their buses. They didn’t switch to electric, they didn’t buy new buses, they just added new engines to the old buses. These new engines ran cleaner with lower emissions.

Based on this, researchers set out to see whether simply replacing an old engine was enough to cause a change in kids' physical health and academic performance.

Study Results

School Bus Retrofitting, Health, and Academic Performance

Figure 2: School Bus Retrofitting, Health, and Academic Performance. If a school district gave 100% of their school buses new, cleaner engines, we would see improvements in Aerobic Health and English test performance. Based on the results of the study, researchers estimated that a 100% switch to modern engines will add 4% to an average child's VO2Max and a 5% increase in English test performance.

Researchers found that kids in schools that retrofitted their buses with new engines showed significant improvements in their health and academics.

Based on the numbers that they saw, they calculated that if a school district were to replace 100% of all bus engines with newer engines, they would expect to see an approximate 4% increase in an average kid's VO2Max, a key metric of aerobic fitness.

Similarly, they found that English test scores also increased significantly. They estimated that if all these buses were retrofitted, we should expect to see kids increase their English test scores by around .145 standard deviations. This means that for an average kid, they would expect to see a 5-6% increase in their percentile rank.

What is VO2Max

VO2Max refers to the maximum amount of oxygen that your body can use during intense workouts. This metric is a key indicator of aerobic fitness. Being able to breathe in and use more oxygen allows you to run, cycle, or swim better.

Evidence Score:

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Sample Size - This study had a very large sample size across Georgia.

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Data Collection - This study used objective metrics that were relevant to health and academics. These metrics did not rely on survey data.

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Confounding and Bias Potential - This study had significant potential for bias. For example, schools that invested more in buses may have invested more in students as well. The two sets of schools were also not closely matched at baseline.

Air Quality and English Test Performance

Air Quality and English Test Performance

Figure 3: Schools in Michigan with higher air pollution had lower English scores. Bars above represent quintiles arranged from lowest air pollution to highest air pollution. The schools with the most air pollution had 37% of 8th grade kids failing to meet academic standards in English. This was significantly more than those in the least polluted schools, which only had 19% of kids failing to meet standards.

This data is consistent with previous research that found significant links between air quality and academic performance.

Kids in Michigan who lived in areas with low air quality were significantly more likely to fail to meet standards in Math and English.

Evidence Score:

+

Sample Size - This study had a very large sample size across Michigan.

+

Data Collection - This study used objective metrics that were relevant to school performance. These metrics did not rely on survey data.

-

Confounding and Bias Potential - This study had significant potential for bias. Schools in high pollution areas may also have lower income kids or other confounding variables. High air pollution areas may have high noise pollution as well.

Air Quality and Math Test Performance

Air Quality and Math Test Performance

Figure 4: Schools in Michigan with higher air pollution had lower math scores. Bars above represent quintiles arranged from lowest air pollution to highest air pollution. The schools with the most air pollution had 41% of 8th grade kids failing to meet academic standards in Math. This was significantly more than those in the least polluted schools, which only had 21% of kids failing to meet standards.

Key Takeaways

While we cannot say with certainty that old school bus emissions cause lower performance in kids, the data above do point to a significant link that is worth researching.

These studies also show that updating engines in old school buses may be a cost-effective way to improve air quality and potentially kids' health as well at just over $8,000 a bus.

Expert Opinions

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Union of Concerned Scientists

Diesel exhaust has been classified a potential human carcinogen by the U.S. Environmental Protection Agency (EPA) and the International Agency for Research on Cancer. Exposure to high levels of diesel exhaust has been shown to cause lung tumors in rats, and studies of humans routinely exposed to diesel fumes indicate a greater risk of lung cancer.

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National Institutes of Health

Exposure to diesel exhaust particulates is reasonably anticipated to be a human carcinogen, based on limited evidence of carcinogenicity from studies in humans and supporting evidence from studies in

Clearvue Health is not affiliated with above organizations. The information above is provided to highlight and link to useful further reading.