The Wave Theory of Traffic

While driving in the US is down a little bit, traffic and congestion is down a lot.

[T]raffic congestion is subject to a tipping point–what economists call non-linearities. Add an additional car to a crowded road at rush hour, and traffic slows down a bit, and then the “carrying capacity” of the road declines. Traffic engineers estimate that most roads carry their maximum throughput — number of vehicles per hour at about 40 miles per hour — so as traffic slows below that speed, the road actually loses capacity and goes slower and slower, producing a traffic jam.

When we were touring we were incessantly sitting in traffic, usually at 6 PM when we were late for load in or at 3 AM when we were driving at night to avoid traffic. The guys up front staring blankly out the windshield at the cars and trucks snaking in the distance, the crushing reality of the digital clock cutting short soundcheck and possibly dinner. The guys in the back were only mildly aware that we weren’t moving, knowing that while we should be somewhere by now, we weren’t, and it only really mattered if we missed dinner, anyway.

Once in a while, there would be a pileup or emergency vehicles or construction. But more frequently, we’d be sitting in brutal, mind numbing traffic, and all of a sudden, it would clear up and we’d be moving again. We called this phenomenon “Fake Traffic” and eventually worked out a complicated and detailed Wave Theory of Traffic. And now, via Matthew Yglesias, CEOs for Cities have gotten to the bottom of this theory for us. Thank you CEOs for Cities!

The Wave Theory of Traffic