Here's a tragic example from Aaron Naperstek's excellent blog of what happens when urban transportation policy privileges private cars above all other modes of transit (including walking, bicycles, and mass transit).
Following its ignoble debut as a rail corridor for steam-powered locomotives, Fourth Avenue was transformed in stages through the building of underground railway tunnels until it was designated as Park Avenue in 1888. At that point, Park Avenue had extensive stretches of actual parkland that appear to have been automobile-free, as can be seen in the pre-1922 photograph looking north from 50 St. It must have been a city dweller's paradise; imagine relaxing on a bench along a charming brick pathway surrounded by grass, shrubbery, and glorious civic architecture. After 1922, this idyllic landscape was ripped out to make room for automobiles.
What in fact seems today a far-fetched dream was once a reality. Well, why can't we be more demanding of our city planners and elected officials and more radical in our proposals? Why does a street have to be noisy, ugly, and dangerous?