Sure but that means your argument for building a new highway needs to be "it will get more people where they are going" and not "it will reduce congestion", and

Sure but that means your argument for building a new highway needs to be "it will get more people where they are going" and not "it will reduce congestion", and you definitely can't pull any "if people are able to get where they are going faster it will reduce emissions" nonsense, which does get brought up. And if the problem you are solving is "get more people where they are going" all of a sudden highways no longer look like a cost-effective solution at all, and public transportation looks _a lot_ better. A lot of highway expansion gets justified by the claim that it will reduce congestion, despite a huge amount of empirical evidence and theoretical justifications (e.g. TFA) that it does not.