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Comment by dumbmatter | Hacker News Reader

I still don't see why "Adding 10 percent more road capacity leads to 3-6 percent more vehicle miles in the near term and 6-10 percent more over many years" is being interpreted as "ending up with the same amount of congestion".

If public transit or bike lanes would provide a better benefit for the same cost, then I would support them. But that's a separate and complicated discussion. Instead, this article seems designed to mislead people into thinking that expanding roads has literally no benefit, when obviously it does even if congestion remained the same (which it doesn't).

Maybe I'm too cynical...

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Well first congestion isn't linear to vehicle miles. In traffic movement small things have a massive knock on effect. On my daily route to work I see the effect that adding just a few more cars to a road does. Adding 5% more cars doesn't increase congestion by 5% it actually brings traffic to a standstill where it was moving at an effective pace before.

Adding extra capacity can even make the problem worse because of what happens when increased capacity meets lower capacity. Human driver are terrible at going from two lanes down to two. You could say that this is bad design but in cities especially there are constraints that you can't really design around very easily without destroying massive parts of the city. This was done in the past to allow highways to penetrate right into cities but those highways just slowed to a crawl.

As for cost effectiveness bike lanes are a lot cheaper than extra road lanes and very much cheaper than elevated highways. Bus rapid transit is also extremely cheap. That's before you start looking at other cost benefits such as increased health for more exercise and less pollution.

>Adding 5% more cars doesn't increase congestion by 5% it actually brings traffic to a standstill where it was moving at an effective pace before.

That seems to argue in favor of the expansion. The 10% road increase may only lead to a 4% decrease in car density, but that could be enough to bring traffic out of standstill.

In terms of resources used to gain ratio that's terrible. Methods that reduce traffic density are much better than ones that increase it. And that's before you think about what adding extra capacity does to a city. I've lived in quite a few cities in my time and the wider the roads in the city the worse the traffic, pollution and enjoyability of the city.

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