Houston is able to scale even with the space inefficiencies of the car by leveraging sprawl. It is remarkably larger than NYC and has room to grow.
This is the relief valve I mentioned here:
> You simply have to give up and can't grow the city any further. So you have to push people out to other cities.
So a city that can sprawl like Houston, does so, and it grows outward, adding more cities on the edge and becomes effectively a loose federation of many cities, which aids in the transportation issue.
That is a solution that some cities on a plain can make use of to kick out the runway further, but it's unavailable to others with more constrained geography.
Houston, TX is the same population as NYC. Except that it has faster commutes and vastly better housing cost (especially on a per sq.ft. basis).
So we KNOW that sanely-designed people-oriented cities like Houston can scale.