Take pricing off the table and the alternatives are not promising, much worse than tying just one hand behind your back. This is true for almost any public service.
Some years ago, Anthony Downs elaborated and popularized the idea with his "Law of Peak Hour Congestion." Here is a nice summary. Without pricing, extra road capacity will simply attract traffic from other sources (other modes, other routes, other times of day, new trips, etc.). Congestion will not be "solved." The idea is simple -- and the lesson has been ignored a thousand times. Officials are loathe to price but love building things. This is "bi-partisan". Crony capitalism is non-denominational.
Elon Musk has now made another media splash by promising to "solve" LA's traffic problems (which have eluded all of the previous "solutions" for the same reasons) by promising new capacity via a tunnel under the Hollywood Hills. It's big, it's splashy and it's Elon Musk. What could go wrong?
Subways are thought to "work" in NYC for historic reasons. But even there, the costs (in light of U.S. construction practices) have escalated enough to make the whole idea questionable. Would a Musk super subway be any different. There is nothing there that addresses Downs' Law.