Comment by stephen_g

Door-to-door time is going to severely suffer on Uber if (and cars in general) are the only option in dense cities. They'll spend most of their time sitting in traffic.

Once you reach a certian density, cars just take up too much space on the road for the number of people they carry, and the only way to meaninfully reduce traffic congestion is to take people out of cars and onto higher-capacity transit.

We already know ride-sharing can't scale up unless your city has super low population density.