Every day, almost a million LA County residents wait at busy city intersections for the bus. A new UCLA study finds they’re breathing high levels of vehicle exhaust because of it.
Intersections are particularly bad places for people to hang out, because when cars accelerate from a stop, they emit more pollutants than when they are driving at a constant speed.
The UCLA researchers wanted to know how much vehicle exhaust bus riders would be exposed to if bus stops were re-located to the middle of a city block, where cars are usually cruising along instead of starting from a standstill?
To find out, they grabbed particulate matter sensors and climbed into electric cars. They drove dozens of slow laps around six different city blocks in Los Angeles, taking air pollution readings at head-height.
What they found surprised them: relocating a bus stop just 120 feet from the center of the intersection could slash emissions exposure in half.
“We expected there to be a difference between concentrations of fresh vehicle emissions near the intersection compared to further away,” said lead researcher Suzanne Paulson, an atmospheric chemist at UCLA. “But we didn’t know how much of a difference there would be.”
Maria Vallecitos, who lives in San Pedro, does not have a car and takes the bus a few times a week. She was not surprised by the findings.
“Sometimes I’m at the bus stop, and I feel fine,” she said in Spanish, standing on the noisy corner of West First and South Gaffey streets. “And then suddenly, cars or buses stop. And when the exhaust comes out of the cars, you smell it, and you start coughing.”
Breathing vehicle exhaust is, not surprisingly, bad for you. It can aggravate asthma and other respiratory and cardiovascular problems. Frequent exposures, like those experienced commuting by bus, may increase the risk of chronic diseases. Diesel exhaust, in particular, is a carcinogen. But because exhaust particles are so small and light, they are not covered by EPA's particulate matter standard and are essentially unregulated.
The LA County Metropolitan Transportation Authority wouldn't comment on the findings. But the agency considers bus stops at intersections to be safer because they are near a crosswalk. Mid-block bus stops have higher instances of jay walking, according to an agency spokesman. They also require more walking when transferring between lines, which is an issue for disabled riders.