1 1. Rolling Bridge

Background: UK-based design firm Heatherwick Studio created this 39-foot timber and steel bridge in 2004 to act as a walkway over a small section of London's Grand Union Canal.

Why It's Innovative: A hydraulic system built into the bridge's handrail allows it to retract and curl into an octagon. The retractable design allows for boats to cruise through the canal unobstructed, and the bridge rolls up every Friday at noon.

Donald MacDonald, an architect with more than 40 years of experience who has worked on over a dozen bridges, tells PM that, "this bridge represents an experimental gesture, and it's really complicated for what it does."