Reminds of the Navy Pier Flyover in Chicago, a half-mile long bicycle/pedestrian bridge that took seven years and $64 million to construct[1].

Not saying that this project was simple by any means, but why did it take seven years to finish? For comparison, the Sears Tower, arguably Chicago's most iconic building and at one time the world's tallest building, only took four years to complete.

[1] https://blockclubchicago.org/2021/05/10/navy-pier-flyover-a-...