The U-shaped steel bike rack is surely the unsung workhorse of urban street furniture. U racks - more accurately, upside-down U's - are so plain, so recessive, you don't really see them until you need one. (And then, invariably, they're full.) U racks are cheap. Their streamlined form takes up very little space. Except in extreme circumstances, they're also indestructible. All that makes them a nearly perfect design.