Alon Levy, who blogs frequently about mass transit, hates on the Hyperloop:
My specific problems are that Hyperloop a) made up the cost projections, b) has awful passenger comfort, c) has very little capacity, and d) lies about energy consumption of conventional [high speed rail]. All of these come from Musk’s complex in which he must reinvent everything and ignore prior work done in the field; these also raise doubts about the systems safety that he claims is impeccable.
Tyler Cowen notes that you “can already fly LA to San Francisco in about an hour”:
Flying is carbon-negative, but of course building and running a hyperloop would be too. In any case, it is hard to believe that a hyperloop is the marginally cost effective way to reduce carbon emissions, compared to say shutting down some more dirty coal or pricing traffic congestion.