I picked those examples as jobs that I don’t imagine require any specialist training (at entry levels), with requisite skills being learned via on-the-job training.
I don't work in any of these areas, but I hesitate to presume that just because they are considered "blue collar" jobs they require no training.
Here's a pamphlet [1] put together by the Federal Highway Administration, called "A Playbook to Build Tomorrow's Highway Construction Workforce". On the first page you learn that there is a shortage of heavy equipment operators, cement masons, and iron workers. These jobs look non-trivial to me. I don't think you become a cement mason or iron worker overnight, or that you can just learn "on the job".
