According to research recently published in the journal Environmental Pollution, bus riders would be exposed to significantly less pollution if bus stops were located away from intersections.
Bus riders can experience wait times (each way) of 25 minutes or more, according to the study.
"The wait often means spending time in some of the most polluted locations in cities, close to intersections where cars, trucks and buses are continually stopping and accelerating, spewing out high concentrations of noxious exhaust," said senior author Suzanne Paulson, UCLA professor of atmospheric sciences. "The exhaust contains gasses and large amounts of ultrafine particles that are essentially unregulated by the Environmental Protection Agency because the EPA regulates fine particles by weight, and these particles weigh so little."
"Our measurements show that traffic-related pollutant concentrations peak near intersections and decrease sharply with distance," Paulson said.
Consequently, the research team believes that exposure to pollutants would be dramatically reduced by moving bus and light rail stops 120 feet from high-traffic intersections.
Using a zero-emissions vehicle equipped with instruments to measure ultrafine particles in addition to other pollutants such as nitrogen oxide and carbon monoxide, researchers drove back and forth across several intersections in LA, Beverly Hills and the San Gabriel Valley, taking measurements every second.
"We then combined and analyzed the data for each intersection to create high-resolution maps of pollutant concentrations along the blocks," said Wonsik Choi, an assistant professor of environmental atmospheric sciences at South Korea's Pusan National University.
"Except in areas with minimal traffic, we always found there would be a significant reduction," said Paulson, who is also a member of UCLA's Institute of the Environment and Sustainability. She added that garbage trucks and other larger vehicles release much more toxic fumes near intersections, when they are starting and stopping.