An autonomous taxi isn't going to make many more trips per day. Every hear of "rush hour?" Turns out most people are moving around the city at the same time of the day, then much less trips in the other parts of the day. (except lunch hour when again all the same people are going to lunch). In the middle of the day the trips people make tend to be different (more likely shopping or delivery: different car type than commuting).

I think most people will try the taxi, but if you already own a car (that is transit doesn't make sense for most trips) you will discover it isn't much cheaper than owning your own car, and your own car is waiting outside when you want to go (one big advantage of owning a car over transit is the car is ready when you want to go instead of having to call or hope one is waiting - if cars need to wait outside your office all day in case your kid gets sick that increases costs). Instead you can just buy a self driving car and then leave your things in the car if you go shopping over lunch - something you cannot do with a shared car.