It’s the everyday engineering wonders that hold a city together. Some of those that Chicagoans take for granted are the city’s double-decker bridges.
Lots of big cities like New York and Tokyo have double-decker spans, but those are long, modern, fixed spans. In Chicago, we make even the short, ordinary, neighborhood bridges double-decker. And we make them move.
The two easiest examples are the Lake Street and Wells Street bridges spanning the Chicago River. Cars on the bottom, trains on the top, and they fold up when sailboats come through.
They really are a bit of an engineering wonder, and something that people in certain other cities call “impossible” until you point out that Chicago’s had these bridges for over a hundred years.