Ridesharing has never been more popular among consumers—or less popular among policymakers.
According to a Pew report last year, 36 percent of Americans have used services like Uber and Lyft; just three years earlier, a third of respondents had never even heard of ridesharing. Meanwhile, after years of largely unchecked expansion, rideshare companies “have entered a new era, marked not by breakneck growth but by skeptical and emboldened regulators.” A New York University study finds that cities across the world are imposing new ridesharing regulations “with increasing speed.”
Among other regulations, such as data sharing requirements and labor protections for drivers, municipalities are considering how ridesharing affects the environment—even if the environmental impacts can be hard to quantify. “Little is known about the effects of this mode on travel behavior and other social impacts, such as public transit use, traffic, and pollution,” write RFF Fellow Benjamin Leard and Peking University’s Jianwei Xing in a new study investigating the environmental impacts of rideshare companies.
Just last month, California announced plans to craft new rules that would encourage more shared trips among riders and increase the proportion of zero-emission vehicles in ridesharing fleets. The plan came after a recent report from the California Air Resources Board estimating that rideshare vehicles emit nearly 50 percent more greenhouse gas emissions per passenger-mile traveled than regular cars. That’s because rideshare drivers spend much of their time driving without a passenger, polluting the air without heading toward a particular destination. The environmental consequences here are substantial: one study estimated that in New York City, rideshares are driving without passengers 41 percent of the time.
But the environmental repercussions of ridesharing are complex and cannot easily be resolved by limiting “cruising” time. Less understood is what types of transit rideshares replace, and that’s what Leard and Xing investigated. If users would have otherwise driven themselves, then the impact of Ubers or Lyfts is negligible—one car is simply replacing another. But if ridesharing is used by those who would have walked or used public transit, then these services cause pollution that would not have existed otherwise. By adding more vehicles on the road, ridesharing can amplify traffic, extend commute times, and increase emissions. In other words, the effects of ridesharing “critically hinge on interactions with current travel modes,” Leard and Xing say.
In their study, Leard and Xing relied on the 2017 National Household Travel Survey, which asks a nationally representative sample of US households which transit modes they use and how frequently they use them. From that survey, which also includes information like the city of residence for each household, Leard and Xing simulate how these households would have traveled if ridesharing were unavailable, and then estimate how many more vehicle miles traveled and greenhouse gas emissions ridesharing has caused.
They find that nationally, the environmental impact of ridesharing has been relatively small: national vehicle miles traveled and CO2 emissions have increased 0.08 and 0.14 percent, respectively. This limited impact likely reflects how ridesharing, which can be prohibitively expensive depending on the route, represents less than one percent of all trips taken in a given year, according to the estimates from Leard and Xing.
But that doesn’t mean ridesharing has affected all US cities in the same way. In cities with relatively low public transit use or where walking is not feasible, the effect of ridesharing on vehicle miles traveled and greenhouse gas emissions was negligible. Where modes of travel besides cars are common, ridesharing has a more pronounced effect on emissions.
Leard and Xing found that in Houston, nearly 80 percent of ridesharers would have used private cars or taxis if ridesharing was unavailable, while in New York City, with its robust bus and rail system, less than a quarter of ridesharing trips would have been taken with a car. A significant number of Bostonians would have walked to their destination if ridesharing was unavailable—but very few San Diegans. Environmental impacts were especially dramatic in San Francisco: Leard and Xing estimate that vehicle miles traveled have increased 1.38 percent and greenhouse gas emissions 2.21 percent since the introduction of ridesharing. These results align with an analysis commissioned by rideshare companies last year, which found that Uber and Lyft rides represent around 13.4 percent of all vehicle miles in San Francisco County, a proportion significantly higher than in other major cities.
The policy implications are apparent: the environmental impact of ridesharing depends on the availability of other transit options. That doesn’t necessarily mean cities with functioning mass transit systems should race to penalize rideshare companies, though. Leard and Xing point out that ridesharing can work alongside conventional modes of transit to help solve “the last-mile problem,” allowing users to quickly hitch a ride to a train stop that would have otherwise been prohibitively distant, for example.
At the very least, this new research suggests that because the impact of ridesharing is so heterogeneous, policy solutions should be tailored to individual cities. As Leard and Xing point out, “[Policymakers] considering restricting access to ridesharing as a way to reduce traffic congestion should do so at a local, city-by-city level and account for the substitution patterns that we uncover.” More broadly, the research implies that policymakers have good reason to investigate the environmental costs of ridesharing—and, if needed, to exert their regulatory might.