Ride-hailing companies Uber and Lyft are transforming urban transportation and eclipsing competitors with convenient, on-demand service. But that convenience carries a distinct climate cost as ride-hailing vehicles emit nearly 70 percent more carbon dioxide on average than the other forms of transportation they displace, according to a new report by the Union of Concerned Scientists.

The report, released Tuesday, zeroes in on a little-known aspect of ride hailing known as “deadheading”—the miles a vehicle travels without a passenger between hired rides—that is responsible for much of the emissions and increased congestion. It also highlights policies that could significantly reduce emissions from the rides.

“While ride hailing trips today are higher emitting than other types of trips, we were encouraged by the fact that they can be significantly lower polluting with efforts to electrify and pool rides,” said Don Anair, research director of the Union of Concerned Scientists’ Clean Transportation Program and an author of the report. “The outlook could be positive with some concrete steps by the companies to move forward, as well as policymakers to support that.”

The report, an analysis of previously released data from ride hailing companies and a synthesis of prior academic studies, first compared the average emissions per trip-mile of private passenger vehicles to those of ride sharing vehicles across seven major U.S. cities. While ride-hailing vehicles were typically newer and more efficient than the average private vehicle, they had significantly higher associated emissions due to deadheading. Approximately 42 percent of the miles driven by ride-hailing vehicles were miles traveled between hired rides with only the driver in the vehicle.

When ride-hailing trips are pooled, simultaneously transporting two or more unrelated passengers headed in the same direction, emissions from ride sharing were roughly equivalent to private vehicles. Electric ride-hailing vehicles had significantly lower emissions than the average private vehicle, emissions that dropped even further when rides were shared.

The report also compared ride sharing to other lower-carbon modes of transportation, including public transit, walking and biking. A prior survey of ride-hailing users across California asked what mode of transportation they would have used had they not used ride-hailing. Approximately 30 percent said they would have used mass transit, walked, biked or not taken the trip at all.

When compared to the average emissions of all other modes of transportation, including private cars, mass transit, human powered transit or simply staying put, emissions from the typical ride hailing trip were an estimated 69 percent higher.

Ride Sharing Cuts Emissions, But Not Everyone Wants to Share

Anair said ride-hailing companies can play a key role in incentivizing drivers to use electric vehicles and passengers to pool their rides.

In Colorado, for example, Lyft subsidized drivers’ leases on electric vehicles and their costs at charging stations. In London, Uber added a fee to all rides to help drivers buy electric vehicles.

Cities and states are also playing a role. In 2018, California passed legislation that will require ride-hailing companies to cut emissions and transition their fleets to electric vehicles beginning in 2023.  

Last month, Chicago began assessing new fees on ride-hailing services that charge more for single-person rides and rides in the city center where they compete with public transportation. The new fee system charges lower fees for pooled rides and rides in areas less well served by mass transit. Some of the money collected from the fees will be reinvested in the city’s public transportation.

Luís Bettencourt, director of the Mansueto Institute for Urban Innovation at the University of Chicago, said it remains unclear how successful these new approaches will be, particularly when it comes to encouraging ride sharing. Despite lower costs already encouraging pooling, only about 15 percent of all rides today are shared, according to the report. 

The report notes how much emissions would decrease if half of all rides were shared, but Bettencourt said that level of ride sharing would be difficult to achieve.

“People want to go fast, they want to maybe have a private conversation, they may not be in a condition where they want to pool,” he said.  

He said electrification could go a long way to solving ride sharing’s carbon emissions. But the desire for non-shared rides and the congestion caused by drivers circling cities waiting for their next ride will still pose significant problems, he said.

“You can imagine a world where all these vehicles are electric and get their power from renewables,” Bettencourt said. “Then you don’t have a carbon problem, but you still will have a congestion problem.”