I'm not sure where you get both "sad" and "preventable" from that documentary. The tragic decline of employment in the US steel industry was completely unavoidable.

The decline of American steel company's dominance between 1960 and 1980 might've been preventable, but the human carnage wrought by automation would've happened in any case.

Watching the documentary, you can see the coming storm. Every video of people working is a prelude to an industrial automation project. And it's no mistake that the documentary ends with an acknowledgment that today's steel workers operate a keyboard and mouse.

The most important lesson from steel is that competitive pressures + new ways of automating things = huge disruptions in the labor market (read: lots of poverty where once there was wealth).

US apparent steel consumption was 97.8 million tons in 2012, the latest date available. That's a bit lower than the 106 million tons in 1968. American steel consumption has declined about 40% per capita. The US steel industry would have had to ramp up exports very aggressively to remain as large a portion of the US economy as it was in the 1960s.

The interstate highway system got passed in 1956. It is now comprised of almost 50,000 miles of highway, and cost almost $500 Billion in todays dollars.

There would have been a whole lot of rebar used in the construction of all the concrete - bridges, overpasses, the concrete sections in Los Angeles and other high volume areas

I wonder how much of that is from import auto sales? Or an overall drop in civic projects?

My top guesses as to causes would be a reduced pace of building/infrastructure construction, reduced steel content in cars, and cars lasting longer.