Some examples of people quickly accomplishing ambitious things together.

San Francisco proposed a new bus lane on Van Ness in 2001. It opened in 2022, yielding a project duration of around 7,600 days. “The project has been delayed due to an increase of wet weather since the project started,” said Paul Rose, a San Francisco Municipal Transportation Agency spokesperson. The project cost $346 million, i.e. $110,000 per meter. The Alaska Highway, mentioned above, constructed across remote tundra, cost $793 per meter in 2019 dollars.

Please send me more entries. (Preferably with sources.)

What's going on?

The physical infrastructure projects enumerated above occurred before 1970 to a disproportionate degree. Why? Some works containing hypotheses: