Current use is limited by cost and convenience.
Self-driving car is likely to fix both so it'll lead to more use of transportation.
This is a good thing. We're currently deprived and if things go well, we'll get more of what we want.
The congestion problem is mostly overblown.
First, maybe with rare exceptions like L.A., the traffic is only bad during rush hour, when people are going to work and getting back home. Other times there's plenty.
Second, the way we drive currently is very inefficient. Just last weak I was walking in San Diego along a street at ~5:30 PM i.e. rush hour.
I just eyeballed but ~80% cars were single person.
Not to mention that ~40% cars were gigantic, because it looks that if people can afford gigantic cars, they'll buy them. And in US they can afford it.
Robotaxis would fix those 2 issues.
The cars would no longer be an expression of personality and a status symbol but a utility operated by an organization focused on practicality and cost, like buses and trains.
It's also very easy to use pricing to force people to use the available resources efficiently during congestion.
Let's say a ride is $10 if you drive in a car alone. $5 if you share with another person and $3 if you share it with 2+ people.
If that pricing delta is not enough, increase the price of to $20 (vs $3) or to $50.
Or provide commuting passes tho employers (kind of like Google buses) where a company pays a $100 to robotaxi company per month and the employee gets to use it for free for commute, but only in shared mode.
The future with robotaxis is much brighter than those doomsday prediction of traffic.