About cars/highways; if you believe electric AVs are actually on the horizon for the near term,then the picture might be, take the AV to the HSR, pick up a different AV at your destination. In that context, providing more auto throughput--which we know induces demand--is not a useful investment. Note here that I don't consider cars as 'evil' per se, so much as inefficient for repetitive trips. Obviously not everyone of us can arrange quick commutes on transit--be it to an office or a factory--but certainly the thousands who cross the Bay Bridge (my local example) are NOT all people who need those cars all day to circulate in SF--most simply park. (And FWIW, when I was selling books for Random House in NYC half a century ago,there were NO bookstores worth calling on, not immediately accessible by subway, or a quick bus ride from the nearest subway station. Driving and then parking, particularly in Manhattan, OTOH was insane.
Yesterday, I ended up on BART leaving Civic Center just after 5PM--i.e. height of rush hour. While I was one of many standees, the 9 car train was NOT crush loaded. Another transbay tube and we will have enough capacity for the jobs in the offices in the CBD AND all of the other reasons to commute.
Thus, if considering increasing travel from the LA basin to Las Vegas, in my view, real HSR with the necessary feeder routes is where the money should go rather than more acres of tarmac.