This seems to me to be a timely warning, but a pessimistic forecast. While I agree that your scenario is one likely outcome, autonomous vehicles also present tremendous opportunities for administrative corrections to these issues. Some examples of why I feel like you’re being too pessimistic:
(1) You can control the vehicle flow to city centres with enforced taxation on a micro-level. Each block of each road can have its own taxation level, making drives into city centres an unneccessary luxury. This can come on top of time-differentiated pricing and ride sharing discouts, which will be another necessity to optimize fleet utilization. We will order our ride and get an instant price regardless, so this will be seamless. Handicapped passengers can be granted excemptions from certain forms of taxation.
(2) Autonomous vehicles will require less space per vehicle, especially as communication between the vehicles improve. Where we today communicate using turn signals and our placement on the road, future vehicles can communicate their destination, route and both planned and current speed to other autonomous vehicles in their vicinity. This allows much more efficient road capacity utilization and will eliminate road congestion. Add in the reduced demand for parking space and reduced demand for commercial property as autonomous delivery vehicles will move commerce to near instant home deliveries, and your city centres will have freed up plenty of space for pedestrians and bicycles.
(3) Your premise in your post that “Obviously, there will always be people who use private cars to move around” has no real consequences in my opinion. I envision this to be similar to how some people have personal jets today. They don’t fly them themselves, but they own them because they prefer to, it allows them an extra level of comfort and convenience, and they can afford the luxury.
In conclusion, a lot of your concerns can be addressed through taxation and policy. However, this requires a deep understanding and foresight into what the future may look like from policy makers. You and others in your profession play a very important role in building that understanding and foresight, so for all our sake, I wish you all the best in your endeavours.