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This article seems like a gross oversimplification. There are a lot more variables at play here than just what people tend to do with extra capacity. Terrain an
by sologoub 12y ago
This article seems like a gross oversimplification. There are a lot more variables at play here than just what people tend to do with extra capacity. Terrain and flow dynamics, as well as driver behavior, have a lot to do with it.
Take 405 in West Los Angeles for example. On one side it has the Sepulvida pass with very steep decent going south and ascent going north. It is crossed by I-10 going to Santa Monica and Downtown, a little further in 90 goes to Marina del Rey, and then exits for LAX.
If you examine this section as an example, you have number of people either trying to get in or pass through this section during commuting hours. From the north, the sepulvida pass makes people slow down as they climb the hill. Not exactly sure why, but many drivers seem to be afraid of it. This recoils through the rest of the traffic, as each incremental car slowing down results in the car behind it slowing down slightly more.
Once you get down the hill, you have people exiting and entering with very short distances to decelerate or accelerate, causing more slow downs.
On the other side, you have a similar dynamic, but people are also trying to merge to or from 90 and I-10. With majority of the traffic heading either to Santa Monica, West LA, Century City or Hollywood/Downtown/something in between.
The city has recently completed a major expansion on the 405 in that area adding a carpool lane, but more importantly changing how you merge to/from several of the exits, including Wilshire blvd and I-10.
In my observation, the carpool lane did relatively little, but the smoothed exiting/entering with enough time to accelerate shifted the bottleneck from before Wilshire blvd, frequently spilling past the 90, to no ending around Wilshire.
The flow restriction now seems to be the dreaded 101 interchange, with a huge amount of traffic stuck in the Sepulvida pass. As the result, I can not get from the 90 to I-10 in about 10 mins, whereas before it was easily 30.
Point being, that if you maintain road size (or marginally improve it) and optimize the flow, you get a lot better returns.
- gr3yh47 12y agoapparently, correlation is equal to causation[1] [1]entire article
- moskie 12y agoI don't think that applies. Isn't the point (or one of the main points) of building more roads to make traffic congestion better? The study in this article shows that that doesn't pan out.
- lmm 12y agoCorrelation may not imply causation, but non-correlation is pretty strong evidence for non-causation.
- moskie 12y agoWell, sure, the article doesn't fully describe the intricacies of the situation... but neither do your anecdotes. But nevertheless, the study mentioned in the article does show that building more roads does not make traffic better: > "[the researchers compared] the amount of new roads and highways built in different U.S. cities between 1980 and 2000, and the total number of miles driven in those cities over the same period. “We found that there’s this perfect one-to-one relationship,” said Turner. If a city had increased its road capacity by 10 percent between 1980 and 1990, then the amount of driving in that city went up by 10 percent. If the amount of roads in the same city then went up by 11 percent between 1990 and 2000, the total number of miles driven also went up by 11 percent. It’s like the two figures were moving in perfect lockstep, changing at the same exact rate."
- sologoub 12y agoI'm pretty sure you missed the entire point of my comment. Basically with highly concentrated areas of work for people living in the sprawl that is greater LA, the bigger gains are not in bigger roads, but in facilitating better flows in existing corridors. LA freeways have a lot of room for optimization, the big problem is always cost and lag in implementation. The above "anecdote" took 2+ years to be built. If you have never experienced 405 in West LA, I suggest you visit :)
- vitd 12y agoHonestly, it would have been hard to make the Wilshire exit/entrance any pathologically worse. It was one of those ramps where the entering cars have to merge with the exiting cars and everyone was entitled and freaked out about it. (I used to live about 4 blocks from it.) It was awful, so I'm glad they've finally fixed it.