A new study from the Booth School at the University of Chicago estimates that ride-sharing services like Uber and Lyft have become significant contributors to the rise in fatal traffic accidents. They are not only increasing street congestion and hurting transit companies, but are also killing people.

An article from Streetsblog notes that the increase in congestion is partly due to drivers spending 40 to 60 percent of their time circling without passengers, known as “deadheading.” Uber and Lyft have increased traffic deaths by 2-3 percent nationally, which is 1,100 additional deaths per year. These companies are supposed to help solve transportation problems, but evidence shows they are making many problems worse.

Cities with high Uber and Lyft usage had more pedestrian deaths, more traffic deaths at night, on weekends and overall, compared to other cities. Drivers for these companies receive little training and are relatively inexperienced compared to the taxi drivers they replaced. There is little quality control in the companies. Uber has been slow to impose limits on drowsy driving comparable to those for other commercial drivers.

Finally, this year, they imposed a rule requiring drivers to take a six-hour break after 12 hours of straight driving, a much weaker standard than the federal government requires for most commercial drivers.