In almost any major city, one finds traces of phantom highways, either actual or invisible, from the off-ramps that used to swoop down onto the Bund in Shanghai to Seattle's "ramps to nowhere," all the remains of the rejected R.H. Thomson Expressway. The massive urban systems that were never built raise interesting questions: Would those cities today be better off—and in what ways—had those highways been built? (There is no study of this question comparable in rigor to Robert Fogel's work imagining the surprisingly low costs to U.S. economic development if railway systems had never been built; there is, however, interesting research from Brown University economist Nathaniel Baum-Snow, who has estimated that "that one new highway passing through a central city reduces its population by about 18 percent.") Would a Paris crisscrossed by expressways even be Paris—or just a through-route to some peripheral suburb—had it succumbed to George Pompidou's imperial visions of making the city "adapt to the automobile"?
The best answer may come from those cities that have torn down portions of postwar expressways: Predicted transportation cataclysms have generally not materialized, and new urban value has been added—vibrant new spaces rather than the social anomie depicted by painter Jeffrey Smart.
And never-built highways speak from the grave in another way: Writer Sara Mirk points out that "when current transit planners visit from exotic Houston and D.C. to admire Portland's progress, what they are really admiring are the roads not built—freeways erased from the maps decades ago." The converse is the now-erased social geography that lurks beneath many a seemingly innocent and inconsequential highway cloverleaf; in Miami, as historian Raymond Mohl notes, one single massive interchange wiped out thirty square blocks—roughly 10,000 homes—of Miami's Overtown, known as the "Harlem of the South."
Urban highway demolition continues—federal dollars may help knock down highways in New Haven and New Orleans, among others. But as urban planner scholar Robert Cervero points out, "it would be wrong to conclude that elevated freeways are increasingly relics of a bygone era. Tampa, Florida, for example, recently opened six miles of an elevated freeway (three lanes plus a breakdown lane on each side)." In places like Mexico City, already home to the massive double-decked Segundo Piso expressway, plans are currently afoot to build a new urban expressway—the Supervía Poniente—even though, as La Jornada points out, it will, for all its costs and civic disruptions, benefit only a small percentage of the population. Is Mexico City rationally planning a path to the future? Or pursuing a route that has already been deemed a dead-end in the world's greatest cities?