That is a choice we will make. 
If we have the kind of population growth that's predicted, we have a huge opportunity to build a city where walking and transit can work for the vast majority. 

It doesn't take Manhattan level density. Cap Hill, Wash Park, Baker, most of the neighborhoods along Colfax have it. A mix of houses, townhomes,  apartments, mixed use buildings, neighborhood commercial strips within walking distance. Walkable. It's the way cities have been built for thousands of years. It's not that hard. It's not out of reach. I don't know if we'll have the political will to get there, but I know it's possible.