The Oncoming Lane Frees up First

You crest the ridge on this highway and notice three or four vehicles ahead of you slow down, evidenced by their brake lights coming on as they reach the far wall of the valley. Down you swoop, then up, and you come to a stop behind those vehicles; one of them, a truck, has its 4-way flashers turned on. All have come to a stop.

There is some sort of stoppage ahead of you; probably a collision. A collision between two vehicles or else a car has slid off the snowy road.

Seconds pass, and after ten minutes conversation dies. All of you are wondering how long you'll be stuck here, and some of you are regretting downing that third coffee before the taxi collected you two hours ago.

After fifteen minutes a small car goes zipping past you in the other direction. I remark that one of us, up ahead over the rise, has elected to make a U-turn out of our line-up and is now heading back the way we all came. A second car zips past us, a third, and I begin to think that perhaps the collision site is cleared.

Sure enough, the northbound tide is in full swing; these aren't U-turns; these are people relieved to be able to drive at the speed limit on what, to them, is an open road.

We are stationary; envious.

One of us comments that the northbound traffic is being freed, whereas we are condemned to stay here.. I think that that is a bad assumption, and a minute later am rewarded with our forward motion in a southerly direction.

What happened?

Look at any block of stationary vehicles, perhaps at a red stop-light. Each vehicle starts moving a second or two after the car before it has moved away. There are, perhaps, three hundred cars in our line-up, which means that at twenty feet of space occupied by each vehicle, there must be 6,000 feet of vehicles, and each vehicle is leaving at the rate of thirty per minute.

6,000 feet is well over a mile, and so the first vehicle in the other lane will be passing us at 60 miles an hour within one minute of its starting movement. 60 miles per hour is a mile a minute.

But the three hundred of us, departing at the rate of thirty a minute, will take ten minutes to free us up.

The northbound traffic will be zooming past us for nine minutes or so before we, at the tail-end of the three hundred cars, can begin to move.

You doubt me?

The three hundredth vehicle northbound in the blockage will be saying what we say when the first of our three hundred cars, liberated, begins zipping past them.

The two lineups are 300 vehicles each, and are symmetrical in their situation.

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