Why not small (ish) self-driving buses that run very regularly (you shouldn't wait more than 10 mins for one) that people can hop-on hop-off. Networked so that you can get from one side of the city to the next in no more than 3 hops.

Big enough also to takes prams/buggies/bicycles/luggage/large shopping items, so that people can also get to do many of the normal things they would do with their day and still use public transport.