Building More Highways Will Reduce Traffic Congestion

Think of traffic congestion as the cost of using a freeway. Now think about the forces of supply and demand in a normal market. If you increase the supply of product X, more people will consume product X. But that's only because the price is now lower. It would be wrong to claim that the increased supply of product X caused so much more demand that the price rose right back up to the original level. Indeed "demand" doesn't increase at all, rather quantity demanded rises due to the lower price.