> Right, but this usually turns into the argument that we shouldn't add new capacity because then it would be used, and that's such a staggeringly stupid argum

> Right, but this usually turns into the argument that we shouldn't add new capacity because then it would be used, and that's such a staggeringly stupid argument that I cannot comprehend the confusion of ideas that would lead someone to embrace it. Well... I hope this explanation is soothing then. It's about what the investment in more capacity is meant to accomplish. Accommodating more cars? Sure, but why did you want to accommodate more cars? To move more people from A to B, more comfortably. Now, what happens when you create this capacity is that it gets used to the same point it did before you built it, until moving people in cars through roads becomes untenable due to congestion. By making it temporarily better, you put more vehicles on the road, made it more viable to move to the suburb, and allowed the problem to grow. So, describing this phenomenon as an argument not to build more capacity for cars as it won't have the expected pay off in quality of life for people is important. It can and often is an either/or building more capacity for private cars or allocating that money to public transportation.