a book about traffic
Posted by Laura McLay on September 17, 2012
I recently had the pleasure of reading the book Traffic by Tom Vanderbilt (@tomvanderbilt) as my summer beach read based on the recommendation of a reader or tweep. It is an excellent book. The book is about all aspects of traffic, including operational, psychological, and human factors. Research by several OR professors were included in this book, including research by Anna Nagurney (UMass), Richard Larson (MIT), and John Kobza (Texas Tech). I rarely read books about operations research, so this book was a real treat.
I won’t summarize the entire book, but I will discuss a couple of small parts.
The book starts with a argument for who one should be a late merger at merge points on the expressway, a habit that I picked up after testing a few approaches. The argument here is a mix of traffic theory and psychology. The traffic arguments is that the total throughput at a merge points depends on how people merge. In the US, we tend to merge way before we have to and assume that anyone who violates this rule is a jerk. Germans like to coordinate their merges to increase efficiency. Efficiency is the German Way. It turns out that it is most efficient to maintain two lanes of traffic up until the merge point, where drivers in the two lanes take turns. This is exactly what happens in the merging lanes in I-95 south of DC when driving toward Richmond, where it works pretty well. The total throughput across all lines of traffic is best if drivers obey this rule, and experiments validate this approach. One of the US states changed their merge signs during the summer construction season to urge drivers to merge late and take turns. They noticed a large improvement with throughput. Other experiments had limited success, since drivers ignored the new instructions, merged too early, and were aggressive with drivers who obeyed the new rule. So why do drivers like to merge early? Merging, according to psychologists, is the single most stressful aspect of routine driving. When we attempt to merge, we can’t help but wonder, “What if I cannot get into the lane?”
I enjoyed the part of the book about networks and congestion. One of the main themes was that networks make driving non-intuitive. We have all heard that adding capacity does not reduce congestion. Tom does a wonderful job of making this intuitive. One reason is that more congestion encourages people to take unneeded trips, live farther from work, etc. More capacity = more miles driven = more congestion. Another reason is due to Braess’ paradox, a game theory model for congestion. Anna Nagurney’s work was cited here, and she has blogged about this before, so I will only briefly elaborate. Here, adding a new superhighway that promises shorter travel times to all if it is not congested, then everyone will want to use it (the Nash equilibrium). The congested road will make everyone’s driving time worse.
Another network example dealt with the monorails at Disney that operate on a simple network. For safety, the trains have to slow down if they get close to other trains. If a train catches up to another train in the network, it has to wait for the first train to make its stops. Disney found that service would speed up if they reduced the number of trains in their system by 1.
Traffic is a fascinating book about many OR-related topics. I highly recommend it if you are looking for a book to read. The blog about the book is here. I may write another post or two about this book. Stay tuned.
HT to @iamreddave for recommending the book to me.