Putting stuck floor mat survival strategies to the test

Recent reports of stuck accelerator pedals causing crashes and Toyota’s enormous recall has caused many to question whether or not a vehicle’s brakes are powerful enough to overpower the engine to stop a vehicle, and what you should do if you are ever in that situation. Most experts agree that a typical production car engine won’t overpower the car’s brakes from a stop. But what happens at speed is another question. Since we just happen to have a test track and a few dozen test cars at our disposal, our automotive engineers decided to play MythBusters and put it to a test.
 
Our first two subjects were the Mercedes-Benz E350 and Volkswagen Jetta Wagon, German cars with so-called “smart-throttle” technology. Both will electronically ignore the throttle input if the brake pedal is depressed. With both, we accelerated to 60 mph and then hit the brakes with the throttle pedal still planted to simulate a condition where the floor mat might have stuck it in place. With both vehicles, we were able to safely slow to a stop despite the engine having been at wide-open throttle. After stopping, the engines idled even with the throttle pedal still floored.
 
Verdict: The Mercedes and Volkswagen Smart-Throttle technology works.
 
Next up, we tried our Toyota Venza and Chevrolet HHR. Since these lacked smart-throttles, we proceeded more cautiously. So we decided to start this test by flooring the cars to 20 mph (instead of 60) and then slamming on the brakes. While we stopped both cars, the transmissions downshifted hard, trying to fight us on the way down, and we needed to exert quite a bit of brake pedal effort to stop completely. We then drove a lap around our test course to cool the brakes and repeated the procedure. This time we accelerated to 60 mph before we slammed on the brakes. Again, the engines downshifted and fought us all the way down. But by the time we slowed down to about 10 mph, the brakes had faded so much that we weren’t able to come to a complete stop.  If the driver had less strength or was traveling at higher speeds, they would not be able to slow down nearly as much.
 
Verdict: Most people will likely have a tough time stopping a car using the brakes with a stuck throttle without a smart throttle.

So what should you do if you are put in such a situation? The answer is simple: Put the car in neutral. In each one of the cars we tested, we were able to easily nudge the gear lever into neutral and stop the car quickly. All modern engines have rev limiters that prevent the engine from over revving and damaging the engine. You can safely shut off the engine after you come to a stop. However, we do not advise shutting off the engine while still driving. We tried this with our Toyota Venza—as Toyota suggests—by holding down the start/stop button for three seconds. While this also allowed us to stop, we lost power steering and had trouble maneuvering the vehicle due to the extremely heavy steering.

Related:
Floor mat survey reveals problem with all-weather mats
Toyota and Lexus floor mat recall is official
Toyota advises 3.8 million Lexus and Toyota owners to remove floor mats
Misaligned floor mat may have caused calamity

—Jake Fisher, photo by Mike Leung.

Comments

[Cale]

Wouldn't it be helpful for drivers to practice taking the car out of gear in a safe and chosen environment. The choice to take a car out of gear (or drive) may cause the same sort of discomfort that many feel when asked to press and hold the brake of an ABS brake equipped car. Practice, practice practice... it's important to get comfortable with an emergency technique before there's an emergency.

[Jim]

I took a new Lexus ES 350 out to test the brakes from a high speed roll. At 70 mph I floored the accelerator.The transmission downshifted twice and the engine revved to 5,700 rpm. As the car raced to 80 mph I hit the brakes hard with my left foot. The cold brakes pulled the car's speed down steadily but with a lot of shaking, similar to warped rotors but I expect it was the anti lock brake system. Because I was on an Interstate I let off the brakes at 20 mph and reaccelerated to 80 mph. This time the severely heated brakes would not stop the car. The speed was lowered to 60 mph before the engine began to speed the car back up even though I was exerting well over 200 lbs of force on the brake pedal. A third test indicated no braking was left due to severe brake fade.

My conclusion regarding stopping a car at wide open throttle is that you have one chance. Of course this car had a functioning neutral and an engine kill button but in a panic some drivers might not remember this. Auto brakes are apparently not designed to stop a car at wide open throttle when applied at a high speed roll. The parking brake would be of almost no benefit in aiding stopping the car. Most systems employ a small drum brake on the rear wheels and this would have alreay been heated by the nearby disc rotors.

A 100% fail safe "smart" pedal seems to be a good idea. Neither Lexus or any other manufacturer will be able to control what mats migh be placed in one of their automobiles and the first trip to the car wash could leave you with improperly tethered mats anyway.

[matt]

I've actually had a floor mat stick the accelerator just as these people had, though it wasn't in a Toyota.
The solution was simply to reach down and pull the mat back away from the pedal.
Of course this does take being aware of the situation, cool, rational thinking, and lifting your foot off the pedal.
Changing gears to Neutal is also a great solution.
I also like the idea of a "smart throttle". Here is Anchorage, as well as in California, I often see cars driving with the brake lights on. So the person is not paying attention, or is trying to drive with boots that are too big. I wish all cars came with a smart throttle, as well as a smart driver.

[Michael S]

Gated shifters with a manumatic function can also confuse drivers in panic situations.

I've been in cars with weak detents where the driver unknowingly uses "3" instead of "D". In the case of the deadly ES350, the driver might have been in "S"; moving the gear lever up towards "N" in that mode merely results in an unshift, giving the perception that the vehicle is locking out neutral.

[Mac Demere]

Sorry guys, you're wrong on the second part of this. I've done this test in more than 100 cars, from Tercels to 911s. They all stop. Each one. Every time. With left foot hard on the brakes and right foot hard on the gas, the brakes in a moderately well maintained modern vehicle will always overpower the engine. I've done the test from well north of 100 mph. Makes a godawful noise, but it stops. --Mac Demere

[Will]

I have one concern with this "smart throttle" technology (which seems very clever for the average driver): What about those of us that enjoy heal and toe downshifting? I assume smart throttle will not allow this because you are intentionally applying the brakes and throttle simultaneously?

[Mac Demere]

Just to confirm CR is flat wrong I did the test again. Car A = 2000 Toyota 4Runner with 158,000 miles on it. ORIGINAL rear brake shoes, 50K-old front pads, BFG Mud Terrains (not the grippiest tires), on a damp, curving off ramp. Right foot flat to the floor at 60mph. I stomped the brake pedal with my left foot. It came to a complete stop. (The ABS and the Muds fought for the last 10 mph. But stop it did.) Car B = 2007 Honda Civic with 40K miles with original brakes and tires. Didn't even have to push the brake pedal hard. I'll make a bet to anyone: Show up at GSP airport with $10K in cash. I'll rent the first Camry Hertz or National offers. I'll prove it to you. And you can leave $10,000 poorer. If I'm wrong, you'll win $10,000.

[Arlie]

I actually had the gas pedal get stuck on an old wagon several years ago.

I was traveling probably about 30 mph at the start of the incident and didn't want to overrev the engine by shifting to neutral. I felt I had a few seconds to attempt to unstick the pedal so I jammed my foot underneath it as best I could and pulling hard.

To my surprise this worked and I was able to continue driving normally and did not experience this for the remainder of the time I had the car.

[Karl]

I'm curious if other manufacturers have similar "smart throttle" technology. For example, on GM vehicles equipped with OnStar Remote Vehicle Slowdown, the throttle can be completely overridden electronically (the HHR isn't one of those, though). It seems like it'd be trivial for the engine controller to reduce the throttle when the brakes are applied.

I'm also wondering how effective the emergency brake is at slowing down a car. It seems like you'd want to use both the e-brake and the regular brakes if your car is out of control. An earlier investigation by the NHTSA (I think) pointed out that a wide-open throttle will decrease the vacuum available to power brakes, making it (possibly much) harder to slow down. In this case, an emergency brake that works well is even more important.

[stephen]

I had a full throttle condition in my car once but it was not caused by a peddle problem but my a stuck throttle cable resulting from a nut in the throttle housing. The worst problem is that it started after accelerating up to speed on a very rainy day on the Merritt Parkway in CT. If you know this road you'll know that for much of its length there is no way to pull over especially in the rain with a full throttle. I ran the car to the next exit using the break to control the speed which was difficult off the exit since it was down hill. Once in a parking lot near the exit I shut the engine off and examined it at which point the offending nut was found and removed.

[Jake Fisher]

@Mac – I have no doubt that some vehicles can stop from 60mph (with some struggle as you noted) without going to neutral or shutting the engine off. However, the Venza and the HHR could not in our tests. Either way, the point still stands: “Most people will likely have a tough time stopping a car using the brakes with a stuck throttle without a smart throttle”

[SteveP]

Am I missing something or is no mention made regarding cars with manual transmissions? I assume that in a similar situation, you would shift into neutral (or just depress the clutch) but I wonder what effect that has on the engine. Since many Hondas, BMWs, VW's and Audis are sold with "sporty" manual transmissions (like VW's DSG) it would have been useful to provide some relevant info.

[Alex]

" While this also allowed us to stop, we lost power steering and had trouble maneuvering the vehicle due to the extremely heavy steering."

Give me a break. I've been at the helm of two different 5,000+lb luxury cars (BMW 750IL & Infiniti M45) and had the engines shut down on the highway. No trouble handling the cars whatsoever. To be honest I didn't notice any difficulty in steering whatsoever. Brakes felt less responsive but were more than sufficient in both cases. I've been behind the wheel of even more cars where the power assist for braking wasn't functional and still no major problems stopping the cars. Just the initial moment when you realise it's not there.

It wasn't all THAT long ago that cars didn't have ABS, power steering, speed-sensitive steering, adaptive brakes, power brakes and we somehow managed to get around fine.

Will: The smart-throttle technology also stinks if you regularly do severe-weather driving. Want to dry off your brakes by dragging them a bit while pushing on the accelerator? Can't with the smart-throttles.

[Steve D]

Why not just turn the ignition key back to the first stop? (not the remove keys position, but the intermediate position that allows you to turn the wheel). That will remove power from the engine and allow you to brake nominally. There is enough reserve vacuum in the power booster to brake two or three times with the engine off.