This is only true when there is unmet demand. I have a lot of roads to show you in Western Nebraska that won’t get increased traffic no matter how big they get.
The reason why widened roads increases traffic isn't just unmet demand; demand actually increases. The extra capacity means that people can shorten journey times by using the road, and they then locate their homes and businesses at either end or along the road. The road itself increases demand.
> The extra capacity means that people can shorten journey times by using the road, and they then locate their homes and businesses at either end or along the road
Exactly. So if people are shortening their journey times using the road, then whatever previous journey they took no longer exists. The new road did not increase demand, it relocated already-existing previously-poorly-serviced demand to a new more efficient route.
This is generally a good thing, it's what a successful road project is intentionally supposed to do, and why they are worth spending money on.
This is a mendacious misphrasing of what I wrote.
People move. Businesses move. People are born. Businesses are created. There isn't a static amount of demand. People make decisions based on costs; whether they create a business, whether they have children, where they live, where they work. Roads change costs. If you have a clue about economics, you'll know that when costs change demand changes in all elastic markets.
Roads don't simply move demand around. People make more use of roads when they're cheaper to use. In other words, demand increases.
If you don't understand this, please consult an economics primer. Your argument seems to come from the same place as the ignorant people who think immigration lowers wages.
People are willing to pay a certain amount of time to drive on a road. This is your demand curve. Everyone willing to spend any amount of time driving makes up all of your demand.
Your supply curve is the speed the road can provide. Increase the average speed by removing stop lights, decreasing congestion, etc and you capture more of the demand.
The only way a road increases demand is if people move to a location they refused to consider before the existence of the road. However, non of the analysis on induced demand for roads analyzes this (that I’ve seen on the academic side). All of it is mistaking capturing more of the demand curve for increasing demand because the effect is always immediate.