Your question: "Where in the Constitution is the power for any government agency to regulate private transportation spelled out? "
The answer: Article 1, Section 8, clause 3.
The answer: Article 1, Section 8, clause 3.
Which states: "The Congress shall have power... To regulate Commerce with foreign Nations, and among the several States, and with the Indian Tribes;"
Sorry, I'm not one who reads everything and anything into the interstate commerce clause. I guess you are, though. Please tell me exactly how riding a horse from here to the next town, or driving a car likewise, constitutes "interstate commerce."