They will know that at 7 AM five people on my street need a ride to work and that at 8 AM another ten people need a ride. Those vehicles will be ready and waiting to pick up their owners.
No, they will know that John leaves at 7:00, but today he’s not going til 7:30 because he has to wait for the baby sitter. Bill isn’t going in at all because he’s sick, Mary needed to go early because of an important meeting, and Harry got fired yesterday, so he’s not going in ever. Over a very large dataset (city) those fluctuations might smooth, but over very small ones they do not. So either there are extra cars sitting around ‘just in case’ or you get a text message saying ‘Misplaced demand algorhythm today. We’ll be there in 5 minutes, we hope.’
A few of those and you’ll go back to private ownership, assuming you can afford it.
P.S. ‘every 40 seconds’ is a joke. You can’t get to the connector road to my neighborhood from my house in under two minutes. You can’t get to the nearest highway in under 5. You know what’s growing? The suburbs. You know what’s shrinking? The urban core of the cities.