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Comment by GavinB | Hacker News Reader

"Adding lanes or roads is a short-lived fix. Widen one highway, and drivers from another will defect."

Thereby making both highways have less traffic. The fact that people come when capacity is improved shows that you're lessening the load on other roads!

"Traffic jams are not, by and large, caused by flaws in road design but by flaws in human nature."

Not accounting for human nature is a flaw in road design. Maybe it's just too expensive to account for it, but traffic design is an exercise in understanding driving habits.

Most of the facts in this article are right on and I bet the book is worthwhile, but the writer of the article didn't seem to really think through what he's saying. It's sad when good concepts get ruined by weenie-thinking.

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"The fact that people come when capacity is improved shows that you're lessening the load on other roads!"

False. There's a concept called Induced Demand. (http://en.wikipedia.org/wiki/Induced_demand)

There are many drivers who stay off the roads because the cost of congestion is too high. For instance, people who won't take a given trip if it takes longer than 20 minutes. By increasing road capacity the trip time goes down to 15 minutes. This induces demand from the crowd that desires <20-minute trips. As they join the crowds on the road, they bring congestion back to its equilibrium level of a 20-minute trip.

Even if people bring the equilibrium back up, the extra capacity made their lives better for those whose trips become worthwhile. The idea is not to minimize traffic, but to maximize welfare.

I've always wanted highway response crews to come equipped with unfoldable response screens. Something like a nice 20' screen which would block off the view of the accident from the opposing lane. I've always thought a considerable about of time, money, and perhaps life could be saved by such a policy.

It was nice to finally see an article that explained why I don't see such a thing.

I thought about this, and I don't think it would work. From the response crew's perspective, they want a massive traffic jam, because the cars are moving slower and paying more attention. So the response crews who would have to put up the screen would have an incentive to oppose it.

I sorta agree, and I sorta disagree...

Here in Seattle I've been held up for over an hour on the 520 bridge because of an accident THE OTHER DIRECTION. Having screens would prevent rubber necking on the other side of the highway (with a large cement barrier in between).

Also, I think you can do a lot to the screen itself to increase driver safety. Make it 15' high and entirely yellow/black diagonal stripes and it'll catch driver's attention and get them to slow down. TV and radio educational ads can help too.

What about for opposing lanes? A wreck going the other way is still a sight and both directions will slow to sneak a peek.

The article also mentioned that because of the spectacle, drivers are paying less attention to the road and looking at the wreck, causing secondary accidents.

Then again, a tarp with emergency vehicles is another reason for drivers to slow down and look at something, according to the article. The trick is to find something so mundane that drivers won't bother slowing down.

I think an advertisement printed on the tarp would help to avoid the rubbernecking. We're already great at ignoring billboards and other ads.

Then again... because so many people take the time to slow down and look at the wrecks, why not take advantage of the extra eyeballs and put up signs with ads on them?

That may be the best idea I've ever heard. Bravo.

Paradoxically, adding routes can actually make traffic worse for everyone. Suppose you have two equal-time routes between A and B. If a shortcut is added connecting halfway on route A to halfway on route B (obviously these are not direct-as-the-crow-flies routes with identical speed limits or this wouldn't work) Travel time for everyone increases by 50% (whether you take A, B, or A-B).

I read an article before (tried to find it but couldn't) about a mathematician and [his/her] grad student who had calculated the theoretical maximum cost of this sort of thing and that 50% is the worst it gets, but that's still pretty bad.

This is called "Braess' Paradox"

http://en.wikipedia.org/wiki/Braess'_paradox

Maybe I'm not understanding the article here, but could this apply to the problem with aggressive lane-changers on a highway?

When people (I find this in myself) get on the freeway, it seems like they tend to get clear over to the fast lane right away. Shortly thereafter traffic starts to back up in that lane and the next slower lane looks like it's winning -- so a bunch of people move over, causing that lane to slow and the original lane to speed up. The resultant pattern is an oscillation of stop and go traffic in the lanes in question.

It seems like if this doesn't exactly apply that it at least speaks to what might be going on. I wonder if there has been any research in disallowing lane changes in areas prone to stop and go traffic.

The article about the 50% maximal cost used that exact situation as the attention getter.

>Thereby making both highways have less traffic. The fact >that people come when capacity is improved shows that you're >lessening the load on other roads!

Yeah: on other roads whose traffic problem was not as bad as the one you just expanded.

Other roads with traffic problems bad enough that drivers avoid them if they believe a new alternative has appeared.

Right. For example, say you have a street network with a main street at capacity (IE, stabilized at crowded, but endurably so), and four outlying streets that eventually lead to the same destination, but have a less appealing route (slower, toll stops, plagued with potholes, pick one). The outlying routes may not be crowded at all, but if the main road is widened, it will probably absorb even more traffic from the outlying streets.

You could make this into a graph problem, if you like, or draw analogies to finding parking.

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