New York City’s yellow cabs are iconic of the city itself, though many locals like myself prefer the cost and ease of ridesharing apps like Lyft. Turns out, however, that the yellow cabs can keep the air cleaner than ridesharing vehicles. A study published in Nature on Wednesday shows how New York’s laws to reduce emissions from its taxi fleet has helped reduce air pollution between 2009 and 2015 in parts of Manhattan where the cabs see the highest density. The study authors looked at nitrous oxide and particulate matter, two major forms of air pollution. Starting in 2005, the city began to enact laws to reduce greenhouse gas emissions from its taxis. The Clean Air Taxi Act in 2005 mandated that hybrids join the list of cabs drivers can choose from. By 2008, more than 1,300 hybrids were in the streets thanks to updated regulations that mandated at least 9 percent of the city’s vehicles be hybrids and extending these “clean-air” models’ lifetimes for drivers. The team from Columbia University and Drexel University found over a 15-year period, exhaust emissions dropped 82 percent for nitrous oxide and 49 percent for particulate matter over the six years. That’s pretty dramatic, especially considering that the city’s fleet of 13,500 taxis didn’t really increase the number of miles traveled over this time. The researchers conducted the study by pooling a number of datasets together. First, they had to figure out how much pollution the city’s taxi fleets were emitting a year from 2004 to 2015. They used the same method to look at for-hire car emissions. Between 2009 and 2015, ridesharing vehicles saw only roughly a 30 percent increase in fuel efficiency to 21 miles per gallon while the yellow cab fleet saw nearly an 83 percent increase to 33 miles per gallon. Exhaust emissions aren’t necessarily the best way to measure pollution levels because particulate matter also comes from other vehicles processes from tires and brakes. They estimated the exhaust emissions by looking at average fuel consumption, which can differ in real time. Once they had all that, they coupled that information with public taxi trip data to learn what parts of New York see the most taxi traffic. After they figured all that out, they looked at about 100 sites measuring the city’s air quality levels from 2009 to 2015 to see how pollution changed in areas where taxi traffic was high. The authors note that the drop in pollution isn’t all thanks to New York City rules. In fact, most of the nitrous oxide emissions plummeted before the city made major changes to its laws governing emissions, and the authors attribute the reduction in nitrous oxide emissions to standards the Environmental Protection Agency rolled out at this time. What they credit the city rules with is the reduced particulate matter emissions, which come after 2009 when the city-level regulation became more stringent. None of these local laws impact the cars Lyft or Uber drivers use on a daily basis, though. The authors hypothesize that the city would see more dramatic air pollution reductions if for-hire cars also had to comply with city regulations. “This study provides evidence that air pollution legislation can have real impact,” study co-author Frederica Perera, director of Translational Research at the Columbia Center for Children’s Environmental Health, said in a release from Columbia University. “Even though overall, yellow taxis account for a small proportion of vehicular miles traveled on New York City’s streets, in midtown they account for almost half. Similar regulations targeting other vehicles could make an even bigger difference.” The study shows how regulations can have positive implications for health, though it mostly focused on upper-class bougie parts of Manhattan, where asthma and respiratory issues aren’t exactly an issue. In the Bronx, where childhood asthma rates are among the highest in the U.S. and have been linked to poor air quality, industrial facilities are a major source of air pollution. Taxis are a small piece of the pollution puzzle in the Big Apple, but every little bit helps when it comes to people’s well-being.