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I read the original article discussed by Ars here this morning, and the authors note that they didn't consider the scenario in which multiple intersections exis

I read the original article discussed by Ars here this morning, and the authors note that they didn't consider the scenario in which multiple intersections exist in a connected roadway network. Also missing was any discussion of pedestrians, bicycles, or non-self-driving cars. This is interesting work, and may have applications in some limited settings, but I wouldn't bank on seeing it too soon even after self-driving vehicles are commonplace. Also, as a planner, I feel obliged to point out that the title "To reduce traffic" can never be true. In a best case scenario this would allow more vehicles to use the same amount of roadway resource--i.e. increase traffic. As for congestion, that's widely accepted to be an equilibrium state. So if these intersections were successful at improving roadway efficiency, we'd expect to see the additional capacity eaten up by increased demand.

ccvannorman 11y ago
I used to study traffic a lot, and it's definitely true that eating additional capacity leads to more gridlock assuming the same type of driver. However, consider the freeway case as a starting point. Freeways lock up because of congestion resulting from too many people merging on, causing people to plan poorly/brake suddenly, which leads to a recursive accordion effect, which leads to 5-10 mph stop and go for hours. However, the actual throughput of cars past any one point on the freeway is actually higher at around 40-50 mph (you should get 1.5 - 2x throughput that you get at 10mph), assuming everyone is organized enough[1]. Now imagine pace cars whose sole job it is is to buffer and reduce the negative impacts of poor human decision on the freeway, with a total car increase of only 1-5%. [1] Sorry, I don't remember the source, but I swear I had one a few years ago when I was heavy into traffic.
- dwyerm 11y ago
  I haven't seen the specific study you mentioned, but it is referred to in the book, "Traffic: Why We Drive the Way We Do (and What It Says About Us)" by Tom Vanderbilt. If you are at all interested in traffic, this is a very good book to start with. Mind you, despite being very convincing, I'm not yet a late-merger. I do find myself trying to drive more smoothly, though.

ccvannorman 11y ago

I used to study traffic a lot, and it's definitely true that eating additional capacity leads to more gridlock assuming the same type of driver. However, consider the freeway case as a starting point. Freeways lock up because of congestion resulting from too many people merging on, causing people to plan poorly/brake suddenly, which leads to a recursive accordion effect, which leads to 5-10 mph stop and go for hours. However, the actual throughput of cars past any one point on the freeway is actually higher at around 40-50 mph (you should get 1.5 - 2x throughput that you get at 10mph), assuming everyone is organized enough[1]. Now imagine pace cars whose sole job it is is to buffer and reduce the negative impacts of poor human decision on the freeway, with a total car increase of only 1-5%. [1] Sorry, I don't remember the source, but I swear I had one a few years ago when I was heavy into traffic.

dwyerm 11y ago
I haven't seen the specific study you mentioned, but it is referred to in the book, "Traffic: Why We Drive the Way We Do (and What It Says About Us)" by Tom Vanderbilt. If you are at all interested in traffic, this is a very good book to start with. Mind you, despite being very convincing, I'm not yet a late-merger. I do find myself trying to drive more smoothly, though.