I’m only posting this list because the Dallas High Five comes in at #16:

Background: This five-level marvel of engineering can be found on the outskirts of Dallas, where Interstate 635 connects with U.S. 75. Construction crews, despite the project’s enormous scope, were able to complete the labyrinth of lanes in December 2005, a full year ahead of schedule.

How It’s Unique: As Mahmassani points out, building wider roads is just not feasible in most cities. The solution for Dallas? Go vertical. Certain points of the High Five are as tall as a 12-story building, and about 500,000 commuters pass through it daily. The project required 37 permanent bridges and six temporary bridges to be built. Additionally, 300,000 square feet of retaining wall and 74,000 square feet of drainage pipe run along the interchange. In 2006, the American Public Works Association selected the interchange as one of its “Public Works Projects of the Year.”