Yes, you don't want empty AVs roaming around the streets. There probably needs to be some sort of government intervention to discourage this behavior. Here's what's possible though:
1. Shared ride AVs can deliver multiple people per trip to their jobs, and they can also make multiple trips in the morning, and multiple trips in the evening. Private cars generally take one person, have to sit in a parking spot all day, and then go home.
2. AVs can park relatively far from their destination. After they drop off their passenger, they can go somewhere else to park.
3. AVs, if they can coordinate or be remotely controlled by a parking lot, can park way more densely than normal cars. In a normal parking lot, maybe half of the space is aisles for cars to drive to and from the parking space. If cars could dynamically get out of the way, you would only need a small portion of the space empty. A very simple strategy would be for there to be only room for one aisle for a big parking lot, and all of the cars would just move forward or back to make the single aisle appear wherever it was needed.
In all, this probably reduces the need for parking by maybe 6x relative to human driven cars.
Traffic is just cars times miles. If all your cars are parked far away from their final destination, all you are doing is adding total miles traveled. Those don't just have basic operation costs, but create yet another kind of traffic: Just like how an elementary school creates more traffic than a high school, because pickups and drop offs require more miles than just having the car parked in the right spots.
So instead of, say, having rush hour start at 4pm, with people leaving work, you have a new, free, bonus rush hour at 2, of empty cars driving near the places where they'll need to be picked up. Same thing near any other rush hour: Every added mile kills. It's not even just cars that have this problem: You'll find that in American cities with transit, which often are built with very few key destinations, there are large depots for trains downtown! Bart has no need to use most of their trains most of their day, so you'll find trains that just go downtown and stay there, parked.
What drives efficiency, always, is fewer miles traveled, and having the need for transport be as even as possible. Something like car-centric stadium is terrible: You need major infra to support a game, with many lanes, and many parking places, just to support game days. But then there might be as few as 10 game days a year, so all that extra infrastructure is wasted the other 355 days.
Self driving, rented cars probably make the first worse, and don't really make huge differences in the second. I think that they have advantages: fewer people dying from drunk driving, or someone doing 80mph in a city street running people over, like we had last week in St Louis. Younger people and older people retaining some independence in areas where now they are wholly dependent of others to go anywhere. But the efficiency gains story is a pipe dream. We will see more miles driven, and therefore more total congestion.
First, there's traffic, and there's parking. The claim you're making is that the lack of need for parking in dense areas creates traffic while the SDCs go to park. That may be true, but if the SDCs are delivering say, 5-9 people to work every day between shared rides and multiple trips, the fact that one SDC then has to make an extra drive out of the business district, at the end of the morning rush hour is not that significant.
The hope is also that SDC driving behavior is also a lot more consistent and predictable, leading to more smoothly flowing traffic. Sometimes a few crazy drivers, or worse, drivers that cause accidents, can foul up traffic massively. I'd expect that this would be reduced in a mostly SDC world.
1. Shared ride AVs can deliver multiple people per trip to their jobs, and they can also make multiple trips in the morning, and multiple trips in the evening. Private cars generally take one person, have to sit in a parking spot all day, and then go home.
2. AVs can park relatively far from their destination. After they drop off their passenger, they can go somewhere else to park.
3. AVs, if they can coordinate or be remotely controlled by a parking lot, can park way more densely than normal cars. In a normal parking lot, maybe half of the space is aisles for cars to drive to and from the parking space. If cars could dynamically get out of the way, you would only need a small portion of the space empty. A very simple strategy would be for there to be only room for one aisle for a big parking lot, and all of the cars would just move forward or back to make the single aisle appear wherever it was needed.
In all, this probably reduces the need for parking by maybe 6x relative to human driven cars.