Eli5: it’s said that creating larger highways doesn’t increase traffic flow because people who weren’t using it before will start. But isn’t that still a net gain?

Question

If people are being diverted from side streets to the highway because the highway is now wider, then that means side streets are cleared up. Not to mention the people who were taking side streets can now enjoy a quicker commute on the highway

In: Engineering

Answer 1

When people talk about this (it’s called “induced demand” btw) it’s not the total number of cars on the road that *individuals* care about.

It’s how long it takes for a specific person to get from point A to point B and when you add more lanes that time doesn’t go down, and can counter intuitively go down sometimes.

The most important concept that isn’t just going to be the same amount of cars there were before but the amount of cars on the road will go *up.*

Are there still more people getting from point A to point B? I mean on this specific highway road maybe sure. But if you had a bunch of people that were already getting from A to B on taking public transit and they just switch to cars and it takes about the same amount of time then no.

And if you had a bunch of people that were walking and biking that now switch to cars then well…now they are getting less exercise and polluting the environment more. Hard to consider that a “net gain” that was worth it. Especially because sometimes the traffic is so bad that biking is just as fast or at least comparable.