We won't need as many of them but the ones we use will be almost constantly on the road, 20 cars on the road all the time is more traffic than 100 cars on the road 10% of the time and in people's garages the rest of the time
The biggest change would be the lack of a need for parking. This will allow us to build more densely.
Induced demand economics. Make something cheaper and people use more of it.
If Autonomous cars make ride hailing cheaper we’ll see an explosion in its use, and traffic will increase as cars are space inefficient and road size fixed.
If you are a single person working a flexible schedule (no mandatory meetings), with no other activities planned traffic and travel time are not a big deal. However if you have any life at all you will care about traffic and travel time because you have places to be. Watching netflix is not your goal it is how you kill time that you would prefer to do something else.