Routine design When we think of bridges, it is the dramatic and monumental long spans that come to mind first, especially the lithe suspension bridges such as the Golden Gate and the pure geometric arches such as Sydney Harbour. But the majority of bridges are not such spectacular structures. Most of them are ordinary overpasses, with spans of 30 or 40 feet, carrying roadways or rails across other thoroughfares or over small streams. You see such bridges by the dozen on any drive down the Interstate. They may be lacking in glamour, but they are more representative of a bridge builder's art. The engineering and construction of girder bridges are pretty routine these days, but the bridges are not quite standard items you order from a catalogue. The girders, whether of steel or concrete, are custom-build for each bridge, then trucked to the site and hoisted into place with a crane. The designer still has scope for variation and creativity, and it shows out on the highways: some overpasses are prettier than others. Brian Hayes, Infrastructure: A Guide to the Industrial Landscape engineeringdesignautomationroutine
The axis of movement Moving in the city means constantly changing the axis of movement. In general, lateral movement is confined to a single plane, what’s called grade, the ground level. Because circulation in multistory buildings is fundamentally one way—which is to say from the bottom up—the condition at the top is invariably different from that at the bottom. Rooftop circulation is the domain of Fantômas, of cat burglars and fleeing criminals, of lovers, and of those acrobatic enough to negotiate the gaps between buildings. Michael Sorkin, 20 Minutes in Manhattan A Burglar's Guide to the City movement