That's not the whole picture. The article doesn't directly mention the economic benefits from more people being able to access an area. My guess is that it works something like this:
Let's say you change a 3 lane road to a 6 lane road, and double the capacity. While some people from nearby roads will decide to start using the new road, a lot of increased usage over time will come from the new development that's made possible by the improved capacity. Strip malls will open up, new subdivisions or condos will go in, business centers will open, etc. Which is all fine, but it means that ultimately road usage will increase until some pain-of-driving threshold is reached, at which it'll level out.
Let's say you change a 3 lane road to a 6 lane road, and double the capacity. While some people from nearby roads will decide to start using the new road, a lot of increased usage over time will come from the new development that's made possible by the improved capacity. Strip malls will open up, new subdivisions or condos will go in, business centers will open, etc. Which is all fine, but it means that ultimately road usage will increase until some pain-of-driving threshold is reached, at which it'll level out.