As I was out driving on the recent Yom Kippur holiday (sorry Mom and Dad, but at least I fasted!), I enjoyed what seemed like a miracle: swiftly flowing traffic in the middle of the day on the streets of West L.A.
This was no fluke; there’s a big improvement in the Westside traffic situation every year on the Jewish high holidays. To many, this seems mysterious. True, West L.A. and the southern San Fernando Valley have large Jewish populations, but not that large. How can the removal of a relatively small number of cars be responsible for such a marked drop in congestion?
The reason is the non-linear way in which traffic congestion builds. Each car added to a road creates a very different amount of delay, depending on how congested that road already is when the car enters.
Quite obviously, many cars can be added to a facility without creating congestion at all as the road fills up.
However, when a road reaches capacity, order breaks down very quickly. At that point additional cars impose a comparatively large amount of delay, quite out of proportion to their small numbers. This slows vehicles upstream and ultimately throughout the entire road system.
The bad news? Since the addition of a relatively small amount of new traffic can cause lots of congestion, modest increases in, say, population or economic activity can result in considerable trouble.
But the good part is the converse: getting a fairly small number of cars off the road can greatly improve conditions. This augurs well for solutions like congestion pricing (which I blogged about here and here), because if dissuading only a few drivers will make a significant difference, the tolls may not have to be draconian.
Another option is hoping the Presbyterians do their part by discovering some new driving-light holidays of their own. But that’s pretty doubtful at this point. So why not think about congestion pricing? A small toll can have big effects.
(Hat tip: Martin Wachs, RAND Corporation)