[aero142]

This article does a poor job of representing induced demand so it's can't be trusted to critique it. Traffic and congestion is defined by (number of trips) * (distance traveled). So, if 10 people take 1 mile trips every day, or 5 people take 2 mile trips every day, the traffic congestion will be the same. Induced demand says that by building roads, you enabled people to buy a cheaper house further out of the city, and drive further, thus congestion stays the same. This is true for other trips as well. You might drive further to Costco to get cheaper groceries rather than to your neighborhood store if there is a fast road there.

I think there is a legitimate criticism of induced demand that it usually doesn't provide a tradeoff for when you have enough roads. 0 roads in all size cities isn't the answer. At some point a city has enough roads and should focus on mass transit or other transportation. I've never seen an induced demand argument attempt to define this threshold and why.

[bluGill]

Economics should define that threshold. There are things you cannot do on mass transit - get the lumber to build a new house/apartment for example. There are things you don't want on mass transit (I don't want you to take your smelly garbage to the dump via the train even though this is possible). Thus a small town will need to build roads. However as the town grows to a city eventually the minimum road to all lots is not enough. At this point we need to ask what is more cost effective: building transit in this town or building more lanes. Unfortunately transit depends on the whole system (this applies to roads too, but we started with them!), which means long term transit might have been a better answer, but right now more roads are cheaper.