How Rush Hour Comes to Be
Now that we have a rudimentary model, let's examine some of the prevailing theories about why traffic exists.
Theory of futility: Traffic has always been and will always be a powerful social forcemore people means more traffic.
Aggressive-driver refrain: It's all those #*$^!%@ old people and slow people in the left lane.
Call of the steady driver: It's all those #*$^!%@ jerks trying to pass everybody.
Other suggestions include cell phones, cops, construction, and poor city planning. Each of these assertions comes with relative validity. For instance, a road crew from the Wisconsin Department of Transportation once decided to play a bit of a joke on Minnesotans returning from midwinter holidays spent in Wisconsin; they closed one lane of a stretch of interstate for a mere 15 feet. The roadway was not damaged or under construction, and the crew could be seen on the overpass enjoying the miles-long chain of cars they had created.
While not an isolated incident, more systemic forces must be at work to create the daily grind.
What's important in this discussion is to separate the "incident" causes of problems from those problems more inherent in moving many cars to different places at the same time. While accidents happen, and construction happens, and even poor planning happens, somehow traffic manages to prevail even when none of those things happens.
The conclusion of the Swedish team about the optimum car density revolved around a handful of factors:
People generally drive at a speed that suits them rather than be governed by posted maximums or even minimums.
Recovery from even a minor perturbation in traffic flow (cop, crash, etc.) can take a long time, even once the incident is concluded.
As traffic density increases (more cars in the same amount of road), drivers are unable to adjust for even small variations in traffic flow.
Which leads to the lesson to be learned...