It shows the short term advantages of adding a lane. It pays no mind to what sort of development the new, higher traffic flow will bring, and how that will eventually doom that third lane addition to be just as congested as before. The solution isn’t adding more capacity to roads, it’s getting more people and things off the roads and onto alternative means of transportation.
Make alternative means better (chiefly faster or overall cheaper) and people will adopt them. People might not all be geniuses, but they’re not stupid.
You're assuming that satisfying demand is not a good. You're also arguing that we should wear a hair-shirt until the rapture. (If the alternatives can't compete with relatively good traffic, if they're only used when nothing else works, how good are they.)
