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

Not only that *more* people would drive, but also that people would drive *more*.

For instance, you forgot to buy eggs? The closest grocery store is two miles from your suburban house, but there’s a supermarket a few miles farther that has cheaper eggs, and also you could buy other things. Or people would go to live in farther and farther suburbs, so the congestion that previously happened 10 miles from downtown, now starts 10 miles back.

It’s possible to say that those are good things, because you chose them based on an analysis of cost and benefits, but you’re not taking into account the cost of building additional highway lanes (because you didn’t pay for them directly), or the non-existence of alternatives such as public transit (because you’re not *paying* money).