Last week's answer

Question: When MnDOT planned the extension of Interstate 35 through downtown Duluth in the 1970s and 1980s, local citizens and urban planners strongly resisted a standard open-trench highway because it would completely cut off the historic downtown district from the Lake Superior waterfront. To resolve the dispute, engineers adopted an early precursor to modern freeway lid parks. What structural solution did they design to carry traffic while reconnecting the city to the lake?

Answer: A series of four cut-and-cover tunnels topped with landscaped urban parkland, pedestrian plazas, and rose gardens built directly over the four-lane interstate.

The project was awarded an "Excellence in Highway Design" by the Federal Highway Administration for the designers use of of cut and cover tunnels that "integrated the highway into surrounding urban environment" while creating a "pleasing driving experience." The highway was called the "citizens freeway" for the extensive collaboration with the public. 

Sources: Federal Highway Administration