It’s been a bloody month on Philippine roads, with the huge crash on the SCTEX and the tragic incident at NAIA recently. And while the cause of the SCTEX disaster seems rather straightforward: overworked driver, poor maintenance, possible drug use. the cause of the NAIA crash is less obvious to most people. For us in the motoring press, it signals the return of the dreaded Sudden Unintended Acceleration scare.
I served as a technical driver and consultant for Car of the Year Philippines for several years, doing instrumented performance testing on hundreds of cars, ranging from tiny Suzuki Altos up to commercial cargo trucks. During that time, I assisted former Technical Editor Ferman Lao in a series of tests evaluating possible mechanical causes of Sudden Unintended Acceleration. We found that with the engine running wild, simply pressing on the brake pedal will hold a vehicle in place. On older trucks with rear drum brakes, even with the rear tires billowing smoke, the front brakes are enough to hold things down.
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Most modern vehicles, however, including the one involved in the NAIA crash, feature brake interrupt switches that electronically limit engine speed—typically to just half-speed or 2,000 rpm—when the brakes are held down. Which means that the brakes are never really fighting the engine at full power.
They have interrupt switches because SUA is not a new phenomenon. A spate of incidents in the United States in the ’80s led to the adoption of interrupt switches and transmission-brake locks—which prevent you from shifting an automatic into gear without pressing the brakes—and changes in pedal design to make it easier to tell the brake and accelerator pedals apart.
Yet SUA incidents persisted, even after all possible mechanical causes were eliminated. In the end, investigations showed that people simply confuse the accelerator and brake pedals with each other—a problem that still recurs 40 years later. But if it truly is a driver issue, why haven’t we learned how to stop this?
Bad driving practices are partly to blame. In the wake of the NAIA incident, I’m seeing a lot of talk about flip-flops and two-foot driving. It has not been confirmed whether or not the driver involved was a two-foot driver. He was definitely a tsinelas driver, which is a major red flag. But two-footed driving? There may be a misunderstanding about the kinematic causes of Sudden Unintended Acceleration.
Most automatic drivers drive with one foot. They can only press one pedal at a time, either the accelerator or the brake pedal. When driving with two feet, you have one foot on the brake and one on the accelerator. Each foot has one control to operate.
In SUA, the critical factor is mistakenly hitting the accelerator with your right foot. You will never hit it by mistake with your left foot, not without contorting your body into a pretzel. Scientific studies have shown that two-foot drivers are more likely to hit the brakes in cases of pedal confusion, whereas one foot drivers are more likely to hit the accelerator.
We don’t suggest you undo a lifetime of motor learning and start driving two-footed to prevent the 0.0001% chance of driving your car into a storefront.
Two-foot driving is often discouraged because casual drivers rest their left foot on the brakes, causing excessive wear and irritating drivers behind them as their brake lights flicker every 10 seconds on the highway. There are also safety concerns that they will, in a panic stop, press down with both feet on both pedals, but this is patently absurd, because—you guessed it—that brake interrupt switch would kick in. On modern cars, as shown in our SUA tests all those years ago with both pedals to the floor, that switch ensures that you will come to a safe and undramatic stop.
In the case of SUA, there is no grand battle between pedals. Instead, it is caused primarily by the driver not lifting their right foot from the accelerator because they think it is the brake pedal. Because they have lost track of where their feet are. Because you do not look at your feet while driving, you rely on proprioception to tell you where they are.
While your body usually knows where your feet are in relation to your head, getting in and out of the car, turning to talk to passengers, or simply looking over your shoulder can make you momentarily lose track. Indeed, many cases of SUA occur when a car is turning, suggesting that the combination of arm movement and torso movement can confuse the proprioceptive sense enough to cause pedal misapplication.
The perfect storm of proprioceptive confusion is when turning around and putting the car in reverse, this puts your head, your torso, your hips and your legs all at different angles to the driver’s seat, and having your left arm, right arm and right foot all doing different things at once, causing confusion about where any particular body part is.
Combine this with the bad habit many drivers have of shifting the car into Neutral instead of Park when stopped at a drop-off point or when parked at a convenience store or drug store, and you have a perfect storm waiting to happen.
The NAIA driver testified that he had panicked and tried to hit the brakes when another car drove by. No car was visible in the CCTV video passing in front of him. But there were cars moving beside and behind him. We can reasonably guess that he was looking at those cars, meaning he was getting ready to—incorrectly—back out of his space, not wanting to wait behind the cars stopped in the exit lane.
An attendant standing beside the car testified that they heard the engine revving hard before it suddenly moved. This tells us that one, the driver was already pressing the wrong pedal before shifting into gear, and two, they had left the car in Neutral, not Park, and shifted into Drive—which he thought was Reverse—without pressing the brakes. Once the car started moving, he panicked, pressing harder on the “brake” pedal, not realizing his mistake. The rest, you know. Two dead, dozens traumatized, and a nation asking why NAIA’s security bollards were so laughably incapable of preventing the carnage.
I’ve seen this happen in person 30 years ago, and then over and over again in various CCTV and dashcam videos over the years, of SUVs plowing into drug stores, convenience stores, banks and fast food restaurants. Once panic and disorientation kick in, correcting mistaken pedal application is unlikely.
You don’t have to be utterly incompetent to commit any of these mistakes. Which is why so many cases of SUA involve testimony from the drivers’ families or friends that they are “experienced” or “careful” drivers.
Hence, it isn’t necessarily driver skill, but driving habits that make the difference. Make it a habit to engage your parking brake every time you have to get out of your car or park for any length of time. Make it a habit to ensure the car is in Park every time you come to a complete stop for any length of time. Never mind the people behind you laughing as your reverse lights go on momentarily as you put the car back into drive. Make it a habit to double check your driving position every time you get in the vehicle or every time you get ready to move from a stop. Make it a habit to pump your brakes until you feel resistance before sticking the car in gear and releasing the parking brake. Many people simply lightly step on the brakes, assuming they are on the right pedal, not noticing the lack of that telltale resistance.
And that assumption can be deadly.
In the end, until all cars on the road are equipped with automatic emergency braking, these incidents will continue to happen. But in the meantime, as long as you build good habits, develop discipline, and keep your wits about you, you can at least avoid becoming yet another statistic in the long and sordid history of SUA.
