By Eric DuBois
My post today is somewhat motivated by Sam’s comment last week about his brother avoiding stoplights even if it did not improve his overall drive time. It reminded me of an interview I heard on the radio while hiking a couple years back. The argument was that we could alleviate many types of traffic jams by simply moving slower and more constant rate. There is actually quite a following for this theory and it has proven true so far when tested experimentally.
This works on two levels. On the more objective traffic engineering level, it smooths out the ‘traffic waves’ where cars slow down in a given area (possibly to a stop) and then speed up outside of that area. Essentially, stop and go traffic is a series of traffic waves. This is obviously more gas efficient and safer, and better yet, it actually increases total throughput in that area. More directly to queuing psychology, it means that rather than constantly having to stop, the driver is constantly feeling a measure of progress, which improves satisfaction with waiting in line.
A similar theory holds when traffic is trying to merge, say at an off-ramp. If we leave room and allow drivers to merge with us, then we can all maintain a relatively constant, if slow speed. Whereas by cramming together, the driver must force their way in and that can stop traffic entirely creating a new traffic wave
The big complaint with this is that it means allowing a gap to open between you and the driver ahead. You need a large enough gap that in the time it takes you to reach the next car, they are moving again. Now you may say (and I certainly have), that it is not fair to those of us waiting in line to have this new person drive past us, making us look like fools, and cut in line up ahead. However, that extra car would only add a few seconds to your total commute and by choosing to spite them, you are making the situation noticeably worse for everyone following after.
In essence, we are focused on what queuing theory calls a skip, that is, they are skipping ahead of us in line and a slip- we are slipping further back in line. On a very basic psychological level, this doesn’t seem fair and annoys most of us to no end (some more than others) by its violation of the First-In First-Out service rules we are taught as children.
What’s especially interesting about traffic, however, is that it isn’t a traditional queue. The number of people ahead of us is only part of the equation determining what our what time will be since the ‘service rate’ is dependent on how we act towards each other. By actively cooperating, we can decrease service time and finish service sooner.
In this instance, I think the Nash Equilibrium as it currently occurs enforces that traffic jams will continue to occur. As much as we may want to cooperate and reach a better equilibrium, there will always be the feeling that if we don’t cooperate we can make someone else later deal with that one extra car and come out ahead ourselves.
From a public policy perspective, two ideas have been proposed. One is to send rolling roadblocks of police through those areas at a slightly reduced speed which requires a fair bit of manpower and only seems worthwhile on particularly common or intractable jams. The second is to adjust down the speed limit before the jam, decreasing inflow and again smoothing out the wave. The latter while more practical, also assumes that people will obey the speed limit and we all know how often that happens.
The best case scenario may instead be to find some way to better incentivize cooperation. They have certainly proven effective before in solving congestion problems.