2013 Tesla Model S electric sport sedan [photo by owner David Noland]Enlarge Photo
Two days ago, I described in this article a frightening incident in my Tesla Model S. Approaching a downhill intersection, I inadvertently stepped on both the brake and accelerator pedals simultaneously. The car barely slowed, and it appeared I was headed for a collision with another car.
Fortunately, I realized my error. A second and more accurate stab at the brakes stopped the car, just in time.
I wrote that the close pedal spacing of the Model S had contributed to my mistake--a phenomenon known in the industrial world as “design-induced operator error.” (The fact that I was wearing heavy winter boots also played a role, along with the car's reduced regenerative braking in cold weather.)
I suggested that Tesla could mitigate such double-pedal driver errors by automatically cutting off power to the wheels when both pedals were pressed. But subsequent reader comments claimed that, in fact, the Model S already does this.
So I took my car out again, and with my right foot holding the speed at a steady 40 mph on a gentle uphill, I put my left foot on the brake. Sure enough, the power immediately cut off--and the car slowed normally.
I was puzzled, to say the least. What had happened back at that intersection?
It turns out I didn't test enough variables. Alerted by an astute comment on the Tesla owners' forum, I tried the same test again--but reversed the order in which I applied my feet to the pedals.
While coasting down a steep section of road, this time I kept my left foot gently on the brake, then pressed the accelerator pedal. The power immediately surged from zero to about 50 kilowatts, and the car strained forward against the brake. In other words, I had precisely replicated the conditions of my near accident.
[EDITOR'S NOTE, Mar 26: What follows is the original article, with a new section added, called "Halfway solution," that reflects the author's additional testing and information.
Some readers may ask what Tesla Motors itself has to say about the matter. We don't know. Regrettably, Tesla stopped responding to queries from Green Car Reports some months ago. We have roughly a dozen outstanding questions in to the company, but its Communications staff no longer returns our e-mails or phone calls.]
Like most accidents, it happened fast, with no warning.
I'd just bought a gallon jug of cider at a local apple farm, and was driving my Tesla Model S down the farm's exit driveway, which exits into a 40-mph two-lane suburban road.
The narrow driveway, surrounded by woods, is steeply downhill, and I had to stop at the bottom where it met the road.
Only mild braking
A few yards short of the T intersection, going perhaps 15 or 20 mph, I stepped on the brake pedal.
To my surprise and consternation, nothing much happened. The car kept going. It was hardly slowing down at all.
I pushed harder on the pedal. Still the car kept going, with only the mildest of braking action.
Something was very wrong. I was about to overshoot the driveway and burst out into the middle of the road.
I sometimes have a dream in which I'm driving a speeding car, trying desperately to slow down. I'm pressing with all my might on the brake pedal, my quadricep quivering with effort, and the car refuses to slow down.
2013 Tesla Model S in Florida, during New York to Florida road trip [photo: David Noland]Enlarge Photo
This was a mild version of that nightmare.
Out of the corner of my eye, I could see a car--a white Mustang, as I recall--approaching fast from the left. It was clearly on a collision course if I didn't get stopped in time.
I quickly lifted my foot off the brake pedal and slammed it down again.
The brakes grabbed, and the Model S lurched to a halt with its nose a couple of feet out into the road. The Mustang swerved slightly and blurred past my windshield, its driver probably cursing the idiot who nearly pulled out right in front of him, with potentially fatal results.
I sat there trembling. What the hell had just happened?
Design-induced pilot error
As an aviation journalist, I've analyzed and written about hundreds of small-plane crashes. In most of them, there is no single cause, but rather an unlucky chain of events that leads to disaster. In the end, though, the official "probable cause" is usually determined to be pilot error.
In most cases, that official judgment is correct. Like clockwork, inept private pilots continue to run out of fuel, forget to put the wheels down, botch crosswind landings, and put their planes into stalls.
Car accidentEnlarge Photo
But savvy aviation accident investigators keep an eye out for something called "design-induced" pilot error.
Sure, the pilot may have screwed up. But maybe there was also something about the design of the airplane that contributed to that screw-up.
A plane with poor directional stability is trickier to land in a gusty crosswind. A plane with multiple fuel tanks and fuel gauges makes it harder to keep track of the fuel.
Accident rates triple
Certain types of planes have pilot-error accident rates double or triple that of others--not because they attract incompetent pilots, but because their design makes pilot errors more likely.
And once those inevitable errors occur, certain planes are more forgiving than others. Accidentally stall a Cessna 172, and the plane essentially recovers itself. Stall an AA-1 Yankee, on the other hand, and you must react quickly and correctly to avoid a deadly spin.
It's the same with virtually any other type of human-operated piece of machinery. By their design, certain types of automobiles or chainsaws or anesthesia machines are more likely to be mishandled by their operators than others.
And when those operator errors inevitably occur, the design of the machine can either mitigate the errors.....or not.
2013 Tesla Model S electric sport sedan on delivery day, with owner David NolandEnlarge Photo
My near-accident is a classic case of an odd chain of circumstances that linked up at just the wrong time. But I also believe it's an example of design-induced "pilot" error.
Looking back, it's pretty clear that I screwed up. But if you ask me, the design of the Model S helped induce my error--and then did precious little to help bail me out after I committed it.
Here's what happened:
In a nutshell, I inadvertently pressed both the brake and accelerator pedals at the same time. Quickly realizing my mistake, I was able to stab only the brake pedal on the second try, and stop the car in the nick of time.
As with most plane crashes, my near-accident was the unlucky convergence of a series of circumstances:
I have big feet, size 13. I was wearing clunky winter boots. The Tesla's brake and "gas" pedals are close together. It was a cold day, so the Tesla's regenerative braking was disabled. The driveway was steeply downhill. There happened to be another car coming at high speed.
It all added up.
Before the near-accident, I was aware of the Tesla double-pedal syndrome. That's what saved me from disaster.