Rules of the road

The streets and freeways of California are rife with a particular species: The "traffic expert." These people are not researchers at UCLA or analysts at Caltrans, but normal drivers who, possessed with the small diploma known as a driver's license, tend to consider themselves sage observers of all that goes on through the windshield. They'll tell you they know the "cures" for congestion, who the "best" and "worst" drivers are and which traffic laws don't happen to apply to them (e.g., cellphones should be prohibited, but only when used by other drivers).

But given that most of us have about as much knowledge of the actual traffic code as we do of the laws of algebra (which we also last studied when we were teens), and given that humans are prone to gaps in their perceptual systems and a dizzying array of cognitive biases in their decision-making processes, and given that traffic is a large, fast and dynamic system, of which we can only observe a small part at any one time, we should take the self-styled traffic experts with a bit of amber-tinted caution.

Even though it's true that the average American in 2005 spent 38 hours annually stuck in traffic, we don't know nearly as much as we think we do. Try to picture, for instance, the white stripes that divide the lanes on a major highway. How long would you guess they are? How much space would you say lies between each stripe? When I was asked this question, I guessed 5 feet, with maybe 15 feet between. But in fact, while the exact length varies, the U.S. standard calls for 10 feet, though depending on the speed limit of the road, the stripes might be as long as 12 to 14 feet. Seen from above, in most cases, it is clear that the stripe is as long as the cars themselves. Their ratio to the space between them is generally 3 to 1 -- meaning that for a 10-foot stripe, there's 30 feet of space.

Maybe you guessed better than I did. But in case you didn't, assembled below are a few things about the road that you may not have learned in driving school (or perhaps you've forgotten).

Fast highways are not necessarily more efficient highways. Given a choice, most L.A. drivers rushing home on the freeway would rather go 80 mph than 60 mph. It gets you there sooner, right? Yes ... but as so often happens in traffic, what's best for the individual is not always best for the system: According to repeated studies, the highway as a whole handles more vehicles per hour at the slower speed than at the faster. The reason has to do with the larger "headways," or gaps between vehicles, which grow disproportionately with higher speeds. Most people are extremely surprised to learn that even at its most efficient usage rate, only an estimated 5.5% of the road surface is actually being occupied by vehicles at any one time.