There's studies that show uber increasing congestion. It makes sense when you think about it. Uber drivers are routinely on the road with no passengers. Either waiting or driving to or from picking up a passenger.
You also have more and more people in every growing city supercommuting due to rising housing costs. A lot of these supercommuters are driving their own personal vehicle because they are now living in places where a personal vehicle is a necessity. Once you have your own personal vehicle for local use, it's economically advantageous to use it for commuting to work.
Given all the changes in growing cities in the past 5-10 years, you couldn't even begin to isolate the cause of congestion down to just one cause, but that's what these studies falsely claim because they don't understand the null hypothesis and that correlation does not imply causation.
The biggest study was in SF and was inherently flawed by looking at traffic over years. It's obvious that an increasing population will generate more traffic, and Uber has allowed more people to travel than before. Serving more people isn't a bad thing, it's a natural situation that cities should plan for instead of being constantly surprised by.
Are you sure?
100% of riders, for all rides they take, would choose to use a car if they could not use ride sharing?
Absolutely none would walk, ride a bike, take a bus, take a train, choose not to go?
I have a hard time believing that it's purely a "car I have access to or a ride share," 100% of the time. So I believe some amount of rides are happening that would not have people driving.
Of the drivers for ride sharing, there is some amount of time between trips that they are simply waiting for the next customer. This is time they wouldn't be on the road if they were not driving, and time the person who is using the ride sharing wouldn't be on the road either. So, I also believe that drivers must be on the road more often than the sum of the time they've kept other people from driving.
If drivers are on the road more with ride sharing, and if less than 100% of people using the ride sharing service would choose a method of transport other than a car, I cannot see how ride sharing wouldn't strictly require an increase in traffic?
Uber will add to traffic but traffic always increases anyway. Check any city over any period of time. It's normal. Uber isn't the problem, it's the lack of capacity for a growing population and other viable transportation. For example, look at electric scooters and bikes in big cities that people are using for medium distances instead of cars. That's what happens when there's progress and competition instead of regressive regulation.
The Uber driver has to drive to pick them up. Then once they drop them off, they have to drive to the next fare. Sometimes they even circle around high traffic areas in heavy traffic in order to get to customers faster.
Basically anytime you see an uber driver without a passenger is likely extra car time on the road compared to what those passengers would have done with private cars.