Using ride-hailing services like Uber and Lyft leads to higher levels of greenhouse gas emissions and traffic congestion than driving personal cars, according to a new study from researchers at Carnegie Mellon University.

The problem is that ride-share drivers spend a lot of time "deadheading" (driving alone) without paying passengers onboard, the study found. A 2019 report from Uber and Lyft found that deadheading accounted for roughly 40% of all mileage across six United States cities.

That deadhead mileage increased fuel consumption and greenhouse gas emissions by about 20%, and increased social costs linked to traffic congestion, crashes, and noise by 60%, the study found.

Ride-hailing did lower emissions by limiting the cold-starting of personal cars, but not enough to cancel out the added emissions from the extra miles traveled, the study found.

Uber electric car

Uber electric car

Sharing trips by having more than one passenger in a single car could have a lower overall impact than driving personal vehicles, but it would still be lower than taking public transit, the study found. Pooled rides have also proven less popular than services that allow one passenger per vehicle.

The issue of deadhead miles motivated California to mandate more electric carsin ride-hailing. To get there, it's going to push Uber and Lyft to incentivize EVs.

Both Uber and Lyft have discussed plans to go all-electric, but with little detail on how that will be accomplished. Uber has also announced a partnership with startup Arrival to develop an EV specifically for ride-hailing.