Because this is what my wife and I did. A few months ago, in our effort to better plan a few family trips this year, we booked a long weekend over Memorial Day at a fun resort a few hours west of here. We’re not talking a car ride to Big Bend. We’re talking three hours to San Antonio, where our boys could swim and eat overpriced chicken fingers until they were so tired they crashed in the elevator.
Nothing about this trip was terrible. We left on a Thursday, before rush hour, and as expected, our family had a wonderful time together. At one point, my oldest, Hank, looked at me with tender eyes and said, “Dad, this place is so much fun.” Fist pump.
Then – and this always seems to happen – the trip ended, and we set off for our 3-hour drive home. Of course, the drive home did not take three hours.
You’ve seen this movie before. You hit the interstate, bragging to the passengers in the car because we rallied as a team and got out of the hotel. We didn’t wait on a bell man to come get our bags. Nope, dad huffed his way through the parking lot carrying two suitcases, a make-up/bowling-ball bag and a cooler.
As we pulled out of the resort, my precious wife even glimpsed at me, eyes blinking with pure adoration, and complimented me on every decision we made on departure day.
Ha. An hour into this trip and my precious wife came perilously close to getting out of the car and directing traffic.
If you drive our national treasure of an interstate system, you know how frustration (and blood pressure) brew. You’re zipping along, passing exit signs faster than you can count. Fellow motorists smile as you pass, whistling happy songs and spilling Cheetos on their laps.
Then it happens. You come to a small elevation in the road (come on, we’re in Texas, so how much elevation can we be talking about here?).
Brake lights. Dead stop. The guy with the Cheetos swerves to the shoulder to avoid a 19-car pile-up.
We slog our way down the road for the next nine minutes travelling 8 mph. We look for the blue lights, the ambulance, the fire truck that has shut down both lanes of traffic, and we see… Nothing.
And just like that, we’re back to green-light racing again.
Throughout our now 4-hour drive home, this happened a dozen times. I’ve legally been behind the wheel of a car for the past 28 years, and I’ve never understood why traffic comes to a stop for absolutely no apparent reason. Until now.
It’s a safe bet my readers are much smarter than I, but even if a couple of you have not had the time to do this research, I found a physicist and an engineer who explained exactly why our interstates come to a complete stop without a wreck or Bambi blocking the road. Here’s what I found:
“Sometimes [the stops in traffic] have no cause at all,” wrote an engineer named William Beaty. “They are like sand ripples and sand dunes, and they just appear for no clear reason. They are like ocean waves caused by the steady breeze, or like the waves which move along a flapping flag. They just ‘emerge’ spontaneously from the writhing lines of traffic. In the science of Nonlinear Dynamics, this is called an ‘EMERGENT PHENOMENON.’”
Do what? I caught waves and sand and oceans and breezes and went looking for a Corona.
Down in the comments field to Beaty’s research paper, a guy who goes by the handle of MasterHD added to the discussion with this beauty.
“I’m a fluid dynamicist and throughout your text, you’ve been missing one key point about continuum mechanics. Unlike an incompressible fluid, traffic density can change, and it increases under pressure.”
Besides not even being quite sure how to pronounce “dynamicist,” I got lost right at “continuum,” because I don’t trust any words that have the letter “u” back-to-back.
I’m a journalist who won’t stop until I can find an answer to just about any question, so let me translate all the scientific mumbo-jumbo into something that will serve you well the next time you want to break the bumper off the car in front of you.
According to Beaty’s article, all sorts of things can cause traffic to stop – even miles behind where the actual incident happened. If you come to a merger with an on-ramp, and there’s already a lot of traffic on the road, you’re going to come to a stop simply because there’s not enough room for cars to enter without someone slamming on the brakes.
If you slow down to change lanes, you’re going to cause traffic to stop behind you. Bet you didn’t know that. Let’s say you’re about to miss your exit, so you start slowing down to change lanes. That act of slowing down makes everyone behind you slow down. And in a rearview mirror far, far away, a group of cars has come to a complete stand-still because you tapped on your brakes.
Here’s what happens: Any time there’s a mysterious stop in traffic, it’s because brakes work a lot better than accelerators. You can brake in an instant, assuming your car is street-legal. But once you stop, you can’t get back to 70 mph immediately. You accelerate, then the next car accelerates, and all of a sudden, you have a line of cars behind you – a wave, if you will – that has to go through the same process.
I know this column isn’t usually a traffic show, but for those of us who have been placed on blood pressure medicine because we never understood why traffic can’t just go, there’s your simplified answer.
I feel better now. Can’t wait for Labor Day.