Gridlock shockwave

To get to the Getty Center in Los Angeles, you park at the bottom of a hill in the Santa Monica Mountains, and then take a light rail train up the hill. The views on the way up are pretty spectacular, but descending the view is mostly of the highway. when I visited, lo these many years ago, I actually studied the highway a bit on the way own. I saw a white station wagon in the left lane driving a bit slow for the fast lane. The car behind it (an SUV, I think) caught up to the station wagon and hit the brakes, dropping speed. The next car dropped speed even slower, and the fourth car actually came to a halt. By then the front car had pulled ahead off the front of the line, but the bottle neck was started. One by one cars approached the bottle neck and hit the brakes and then waited a moment for the front car to pull off.

As it happened, I was visiting two friends that day (Hi Chris and Kirsten!), one of whom was then a fledgling economist and system modeler (now he’s a full grown economist). The reason for traffic jams, he argued, was in speed differentials. If everyone drove precisely the same speed, and there were no accidents, there would be no (or at least far fewer) traffic jams. Well, some Japanese scientists have proved him right. the video below gives a proper explanation of the experiment, but basically they had a group of cars drive in a circle at exactly the same speed. But natural variations in driver ability or course construction caused some car to drive slightly slower than another. The car behind it caught up and had to drive slower, and the chain went back for a couple of cars. Then, as the front car accelerated off the end, the jam actually moved backward along the circle like a shockwave, at a speed of about 20 kph. This is the observed speed a jammed section of traffic will move down the highway.

So, one way to solve problems of jam caused by too many cars on the highway would be robot controlled cars. The robots could, hopefully, be counted on to drive at a precises speed more reliably than humans, plus, since they would have faster reactions, they could probably drive in closer proximity, all of which would result in substantially increased capacity for our highways. If I can’t have flying cars, I at least want robot driven cars, OK?

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One Response to Gridlock shockwave

  1. Kirsten says:

    Thanks for the shout-out! Sorry the holla-back is so late….Chris and I were lounging around in Hawaii. Poor us.

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