There’s no doubt that mass transit can make a huge difference in the overall air quality of cities. An increasing number of people are realizing that they can reduce their carbon footprint by riding a bus to and from work rather than being stuck in traffic in a car.
There’s just one problem with riding the bus, and that’s waiting for the bus.
Research has shown that in many cities in the United States and internationally, bus riders could spend 15 to 25 minutes each way waiting for a bus. This isn’t just a convenience issue; it’s a pollution exposure issue, too.
“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 Suzanne Paulson of UCLA, senior author of an article that appeared recently in the journal Environmental Pollution. “The exhaust contains gases 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.”
The good news, according to the researchers, is that moving bus and light rail stops to locations 120 feet from intersections can significantly reduce the amount of pollutants to which bus commuters are exposed.
The researchers came to their conclusions by using a zero-emission vehicle equipped with instruments that measure ultrafine particles and tailpipe pollutants like carbon monoxide and nitrogen oxide. The studies were conducted in several neighborhoods in and around Los Angeles, over a 15-day period from summer into late fall in 2013 and over four days in the summer of 2014.
“We then combined and analyzed the data for each intersection to create high-resolution maps of pollutant concentrations along blocs,” said study lead author Wonsik Choi.
“Except in areas with minimal traffic, we always found there would be a significant reduction [of pollutants],” said Choi.
Traffic engineers believe that traffic flows better if bus stops are located after intersections rather than before. Better traffic flow can lead to less stop-and-go traffic, which would also improve air quality. The researchers caution that although moving the stops 120 feet from the end of a block will improve transit users’ pollution exposure, as long as that distance doesn’t put the bus stop in range of pollution from the next street.
Considering that most city blocks are about generally about 400 by 400 feet in size, it seems like it should be easy to move bus stops 120 feet away from intersections. That doesn’t mean buses won’t park all along a block where a stop is located, but it does mean that theoretically, passengers waiting for their bus will be able to do so in an area that exposes them to fewer pollutants.