Top 5 Myths About Prius Runaway Acceleration

1Myth: Toyota vehicles, like the Prius, put drivers at a high risk.

Fact: Carnegie Mellon University Professor Paul Fischbeck, a risk expert, calculated the risk of driving a recalled Toyota and found that the accelerator problem increases the driving risk by 2 percent—which is already very low. In other words, the chance of dying in a year because of the accelerator problem is about two in a million. This is the same as flipping 19 coins one time each and getting 19 heads. Fischbeck says that you are almost 20 times more likely to die while walking than driving a recalled Toyota.

National Public Radio reported that you are 30 times more likely to get hit by lightning than you are to die in a crash involving a Toyota with a sticky gas pedal.

So, the chances of driving a runaway Prius are extremely unlikely. But still, it’s a problem, potentially a fatal one, and drivers need to know what to do if it happens. The remaining myths and facts come from, a website dedicated to racing news.

2Myth: In the event you encounter a runaway vehicle, the first thing you should do is to turn off the ignition.

Fact: No, the first thing a driver should do is to put the transmission in Neutral. A driver can place the Prius in Neutral by moving the shift lever to the “N” position—to the left side of the shift gate, and hold it there for a second. This stops the torque to the wheels, and gives the driver instant speed control over the vehicle, and allows the driver time to assess what is happening. Shifting into Neutral at full throttle will not damage the engine.

Myth: The start/stop button on the dash will not turn off a Prius while it’s running.

Fact: Pressing the start/stop button does shut down the car, but it’s a backup choice—behind shifting into Neutral—because it will also shut down power brakes and steering. On models with a push-button smart key system, pushing and holding the button on the dash for about three seconds will shut off the ignition system on the vehicle, bringing the car to a stop—even if it’s in gear and moving along the roadway.

4Myth: The brake system on my Toyota Prius is not able to stop the car at speed with a wide-open throttle condition.

Fact: If you apply firm, steady pressure on the brake pedal—use two feet if needed—the vehicle will come to a halt. Do not pump the brakes. All Priuses have a brake system program that reduces gasoline engine power if both the throttle and brake pedals are depressed at the same time. Prius has multiple back-up systems to force the use of hydraulic brakes, in the extremely unlikely event that the electronic brakes fail.

5Myth: The parking brake is effective in stopping a vehicle at speed.

Fact: The parking brake may be helpful, but placing the transmission in Neutral and using firm steady pressure on the brake pedal will be the best way to bring the vehicle to a stop.

  • cjcold

    It would be great to be speeding in a Toyota these days and be stopped by a cop. “Hey officer it just ran away with me”.

  • AP

    There are no clutches in the Prius transmission, which makes it very simple (mechanically) and compact. But it also means that, regardless of the “gear selector” position there is never a mechanical separation between the engine, motors, and wheels.

    Selecting “neutral” in a Prius actually causes the engine and motors to each put out the right amount of torque, so that the is no net driving torque to the wheels. This is done by a computer program balancing the three players (the engine, motor A and motor B), directing them like a conductor in a symphony.

    You would also find there is no mechanical connection between the gear selector and the transmission (the gear selector is too small to move anything mechanically anyway), so even the connection between the selector and transmission is electronic.

    So as long as there are no malfunctions, selecting “neutral” SHOULD stop the powertrain from putting power to the wheels, but you can’t guarantee it, and it is never separated mechanically.

    Please verify this on your own, since I am a GM engineer, I want to make sure people don’t think I am providing any disinformation.

  • Anonymous

    Not sure I like some of your points in myth #1. Not sure I believe the claim on the math:
    1) If you don’t really know the root cause, can you really do a probability of occurance?
    2) If it is a “wear issue” on the mechanical binding, have you taken into account that the probability will greatly increase as vehicles get older?
    3) Wondering on the sampling method. How do you know you are capturing all the reports??

    Anyway, even if I were to give into your stats …. lets take a look…..

    Wow, 8 million vehicles involved, only 2 in a million that you die, so really, we are only talking about 16 or so people losing their lives, from one aspect of their vehicle. Heck, who wouldn’t want to sign up for that lotto??

    “This is the same as flipping 19 coins one time each and getting 19 heads.”
    Again, the odds of doing this are pretty remote. But, would you really want to get into a contest like this, if you knew 16 of the 8 million entrants will “win” and die?

    “Fischbeck says that you are almost 20 times more likely to die while walking than driving a recalled Toyota.”
    Actually, this one I believe, especially if you consider that a run a way vehicle is probably more likely to kill a pedestrian than the driver. Wonder if it used to be 16 times more likely, until he had to factor the run a way vehicles into his calculations.


  • Anonymous

    One other point ….. The stat says dying in a year. If that really is one year, and the vehicles are on the road for an average of 14 years (unless the government does something about it), then … 2 x 14 …. 28 people die per million???? with 8 million vehicles, does that mean 224 people die????

    Sorry, lost in some scary math.

  • Anonymous

    It all sounds easy enough, and we’re all much more likely to get into a normal car crash. Why can’t they just figure out what it is and fix the problem? What kind of a sham is the editor of this article trying to pull? The fact that I’m reading this article, tells me the product sucks, or is that a myth too. Fix the problem.

  • Anonymous

    According to a quick scan of the web, the chances of you dying in a traffic accident in your entire life is about 2 in 100. In the US there are about 40,000 traffic fatalities per year. Divide that by our population, and you get 0.000133% chance of dying in any year.

    Stats are tricky. It’s tough to make sense of them, considering that all cars have an element of risk that’s a lot higher than we usually recognize or acknowledge.

  • AP

    This is odd. My post from 4 hours ago was edited, where I asked the editor to research Myth #2 closer. A bit of Big Brother?

  • Dom

    AP – looks like the editor fixed Myth #2 to reflect your original comment…

  • Site Editor

    Dom is right. We used AP’s excellent clarification–regarding mechanical vs. electronic connections between gears and transmission–and modified the text. The main point is that Neutral is designed to “stop the torque to the wheels,” as we’ve now stated. Whether or not it’s doing that in the cases of runaway acceleration, of course, is still up to debate. The change was made so the primary article presents accurate technical information. We highly encourage debate and differing viewpoints–whatever helps bring a better understanding of the situation, regardless of where the chips fall. Sorry for confusion.

    Brad Berman, Editor

  • AP

    Brad, thanks for the clarification. Who knows whether any particular unintended acceleration case has merit (or any of them, for that matter), but I appreciate your help in keeping the discussion fact-based.

    The company I work for has been through their share of distortion in other safety issues, and I think it helps keep “urban legends” from growing when people understand what can and can’t happen in their cars. Few people really know what’s going on under the hood, especially with today’s cars.

  • Shines

    Anonymous you say:
    Based on the perspective of the statistics you are presenting; life sucks. Who’s going to fix that?
    I’m working on mine… trying to make it better. I am sure Toyota is trying to make their cars better.

  • Another Option

    Another option to consider from Phil Fournier @ Phil’s Auto Clinic

    Push the park button. This is my recommendation as it is very easy and instantaneous. Above 3 miles per hour, your car will not shift into park; it will shift into neutral and the engine will immediately slow down, even if the gas pedal is held to the floor. No damage will result.

  • Mr.Bear

    Anyone else notice that no one has tried shifting to “B” to slow down the Prius?

  • Anonymous

    Mr Bear, i thought of that, but does shifting to B work? my impression of B gear is that it is no different than D position when accelerator is pressed and only different when it is let go. Unless i’m mistaken, it will not react the same way as gears 1 or 2 in automatic transmission. someone wants to give it a try?

  • AP

    Don’t worry too much about risks, Shines. The only way to avoid all danger is to do nothing, which isn’t any fun either. Many people don’t fly because of the remote risk of a crash.

    I think the biggest problem Americans have is that we expect everything to be risk-free. Once you accept that nothing is risk-free, it’s easier to put various risks into perspective. And you realize that you should know what to do when things go wrong – which will eventually happen. Once you’ve done everything to prepare, and drive carefully, you don’t need to worry (what’s the point?).

    Personally, I worry more about the government ruining the economy and our currency, more than being hurt while driving.

  • Cash for used cars

    LOL, the title and the pictures are awesome!

  • tw8s

    Stats ARE tricky; especially when multiple decimal places are involved. My calculator opines that 40.000 divided by 315534716 (likewise a web obtained number) is 1.26 per 10,000, and it is the young foolish and old foolish that make it that high. For you middling years folk it is probably less than half that rate. Whew! We all feel better!
    BTW – Is anybody (independent labs, back-yard tinkerers, engineering school senior projects) doing CAN scan recordings to sniff out this problem, looking for instances when goofy values show up? Software glitches in real-time systems tend to occur at the extremes, such as when a sensor coughs up 23 volts – way out of the normal 1.8 to 2.3 volts. Somebody should have identified at least a half-dozen avenues of ways to fail by now, and be hammering hard to prove they do or don’t lead to catastrophic results.

  • Anonymous

    Now comes the attack the victim stage. Congressional members who have facilities in their state or district, Toyota and investors who believe the whole thing is a auto workers union conspiracy are in full attack mode. It will change when one of their own takes a Toyota speed ride. Guess the state trooper killed with his family just wanted to committ suicide and take his wife and kids with him.

  • Anonymous

    Too much to do to stop your car…good thing it doesn’t happen often. As the vehicles get older, does anyone know if this “unintended acceleration” and difficulty stopping gets worse?

  • AAshraf

    Toyota and the Empire

    Toyota; is it investigation of crime at the accident of Toyota? And what the investigation at the Challenger space-shuttle reached to beyond nothing more than malfunction of some little technical component (seal ring) that had led to the explosion and American national disaster committed by the most sophisticated scientific institution NASA in USA! And where is such investigations at thieving tens thousands of internet transaction cards everyday, while the main cause already known to be the weak vulnerability in the security of the internet transaction itself, and it might be intentional crime because it never satisfactory improved, replaced or canceled? Thousands of examples can be recalled here. One or couple of malfunctions in some technology never had been taken such seriousness; hence it is not the real story.

    I tell you the story. There is something called the imperialistic economic system and philosophy, it was the same all over history. USA is empire right now. Empire’s center doesn’t produce but they militarize, colonies don’t militarize but they produce. That Toyota Perius accident is very connected with the recent Japanese trend to separate from the Imperialistic system and wanted to drive the American military bases from Japan out, so the USA empire center reminds the Japanese about the deal and how the things is working, has it been received? And the Japanese should understand that they will not separate freely without a cost, you are not smarter than your captor.

    Some American street citizen will scream, simple man like me and you; will arise feeling offended and scream, “Our founding fathers and we are against imperialism and slavery; we are for freedom; that is gross untrue”. Perhaps, you are right in what you believed because that what they succeeded to make you believe and deceived. In the past when the economics of human societies was energized mainly by the real materials and confined to that, the emperors were called plainly emperors and they had have clear in eyeball sight crowns and thrones. In our these days, with great leap revolutionary provisions in finance, communications of all sorts, etc. though I don’t agree to the say that it is unprecedented, but I may agree that it is unprecedented within the last little recorded era of few thousand years, there might have been civilizations that even were much developed than what we have today, many basic concepts though haven’t changed yet its face and practice has changed. Economics is no longer a piece of gold or piece of bread; it became piece of notion called paper money, economics have gained lot of flexibility and mobility if not lost its faithful and truthful entity, same thing exactly happened to the entity of the emperors, there is no longer clear in sight a crown and throne, but yet there are empires of crowns and thrones, with great flexibility and mobility, in this phony called modern time we live in the emperors hide in notions as their economy and still I can see their crowns and thrones. Even it is not any longer very easy to track down their language of notions.

    March 16, 2010

  • Shines

    There always have been and always will be greedy and selfish people. This is true in a democracy and in communist and socialist states. There will always be people who strive for perfection and there will be companies and governments that do the same.
    Most people want what is good. Most people try to be fair.
    Some people abuse their power and others try to prevent that abuse. In today’s complex and technological global environment the challenges are greater for both the abusers and those that police them.
    The topic here is hybrid cars and related issues.
    To be fair I think Toyota has tried to be fair.
    As with all human endeavors nothing is perfect.

    But the Prius come close ; – D

  • Mr.Bear

    Shifting to “B” causes high-RPM zero-fuel-flow engine breaking (if the gas pedal isn’t pressed). Essentially it cuts out the flow of gas to the engine and uses the momentum of the car to force the engine to spin.

    If you have your foot on the gas, some fuel will still get to the engine and the car will still go, but you have to put your foot down harder on the gas to maintain a speed. It would be like driving a car with both your foot on the gas and the break. The upshot being, “if you shift to ‘B’ at least you won’t be going 94mph.”

    Additionally, if you shift to “B” it will kick the car out of cruise control. So if its a computer error that is causing the vehicle to accelerate, shifting to “B” may cause the computer to unstick the throttle

  • AP

    Mr. Bear, what you’re saying sounds familiar now. “B” is basically your “Pike’s Peak Descent” mode, where the recoverable kinetic energy is way too much to be stored in the battery, but you don’t want to ride your regular brakes very long (or they’d overheat). While it runs high speed with no fuel, it probably is holding the throttle closed to waste a lot of energy.

    When being efficient is your main goal, sometimes you have to do odd things when the goal is to be wasteful (steep-hill engine braking) to keep the car from gaining speed.

  • Mr.Bear

    I do a lot of hilly driving so I’ve messed around with “B” a little.

    I have to admit I was partly wrong.

    I double checked the cruise control. “B” definitly kicks you out of cruise control.

    However, if the gas peddle is depressed it is no different than being in “D”.


  • Anonymous

    Thanks for clarifying mr bear! it is very helpful to know B gear does not behave same as gears 1 or 2 in automatic transmission.

  • Tony

    What are the odds of dying in ANY car accident while driving? Don’t we ALL know that? Do we you get in the car every day, knowing we might die while driving our car? If you truly answered No to the last question, then the odds are high for you, otherwise it is not any different than anything else we do on a daily basis!

  • Jeff

    How about calculating the odds that TWO problems happened to the same guy in the same car at the same time. He’s claiming that the gas pedal was stuck AND the braking did nothing to disengage and/or limit the engine. I’m sure the Natl Highway Safety people with do some thorough checking on this one, including how well the car was serviced (the brakes could have already been gone if the car is old enough).

  • BC

    The response to myth #4 states that power to the engine is “reduced” when the brakes are applied but this supposed reduction is not quantified. I just tested this on the highway and with the brakes applied I pressed on the gas at the same time and was able to accelerate against the force of the brakes so if there was any automatic reduction in power to the engine it wasn’t noticable to me. I didn’t apply full pressure to either the brakes or the accelerator since I was on a public highway so I don’t know if the brakes would be able to control the car under full acceleration but I know that under at least moderate braking the car can still accelerate.
    To stop runaway acceleration it seems it would be better to fully cut off fuel to the engine when the brakes are applied, which isn’t what currently happens.

  • Mr.Bear

    Tonight on the drive home I tried intentionally shifting to reverse and hitting the park button with my foot on the gas.

    Both resulted in the “double beep” you-can’t-do-that and put me in neutral.

  • Jesse Rudavsky

    Over 217k miles on my 2005 prius and no problems. So far so good. Same batteries.

  • N. Nangap

    I am no expert but I have experienced runaway acceleration, so called, 3 times so far in my 2000 Chev Cavalier. However, I know what causes it. It happened a while after I used my “accel” switch on my cruise control in order to cruise at a higher speed. For same reason, a long while have using the switch the car started to accelerated again on its own. Somehow I realized it was the cruise control and stopped the acceleration just by switching off the cruise. I set the cruise on again and, each time, the unrequested acceleration did not reoccur.

    I am wondering if a similar thing might not be behind the problem with Toyotas. How do I get this idea to Toyota for testing?

    By the way, my cruise control on the same car has now died and this too might be an indicator of the problem.

  • Johan Samul

    “the chance of dying in a year because of the accelerator problem is about two in a million. ” I don’t think this statement justify anything, how can we say two in a million is a small or neglect able figure? if we can able to prevent it then we can save 2 in a million people.

    Above given suggestions are the best to use if we are in a trouble of sudden acceleration, making use of all those neutral, pressing break pedal, using parking break periodically and stopping and starting the vehicle with time gap can reduce the chances crashes. i hope this could be included into the Joshua’s Law courses so that every one could learn and know the possibilities

  • david son

    we need to mandate that every driver need to undergone training on some emergency technique which could us to reduce the death rate.

    Nevada Learners Permit

  • Keiron

    Chances of dying of an accident is very rare but at the same time you have to be cautious while driving.The myths shared by the author are excellent and I would like to elaborate few points on the issue of acceleration.Mainly there is a on delay timer which is responsible for the acceleration and break mechanism.As mentioned in the last point the parking brake of Pirius is superb which means the delay timer is set to very low and hence you can stop the car at a very high speed also.