Video: Consumer Reports demonstrates how "brake override" stops runaway cars
Consumer Reports News: March 23, 2010 08:36 PM
As this new video demonstrates, smart throttle, or brake override, technology can be an effective tool to mitigate the risks associated with unintended acceleration. We have advocated for the adoption of smart throttle or similar technology to ensure drivers can halt their vehicles in a reasonable distance, even if the throttle is wide open. (Read: "Consumers Union calls for changes to strengthen U.S. car-safety net.")
Our ongoing tests with our recently updatedToyota Camry and European models so-equipped from the factory continue to show the benefits of brake override systems, without interfering with normal driving needs or even grin-inducing sporty driving. (Read: " Track test: How does brake-override affect enthusiast driving?")
Brake override is a piece of engine management software that simply lets the brakes take precedence over the throttle or accelerator if both brakes and throttle are activated at once. It's already standard on many cars, including most German imports.
Some people assume that you can always stop a car that's speeding out of control just by hitting the brakes hard, but as you can see in the video that's not always true. And most drivers don't realize that hitting the brakes repeatedly is about the worst thing you can do during a unintended acceleration event because the power brakes in most cars are assisted by a "brake booster" that's charged by a vacuum circuit coming off the engine. An engine that's accelerating isn't producing any vacuum, and repeatedly hitting the brakes will quickly drain away the vacuum reserve, taking the power assist along with it. (Read: " How to stop a runaway car: Five steps that can save your life" and download a pdf of our advice.)
Override's double action: Less going and more stopping
The advantage of brake override is two-fold. By cutting power to the engine, the system slows the car, and simultaneously it lets the vacuum system recharge the power booster. Even if a driver takes several stabs on the brake, the car will progressively slow to a stop.
Maintaining power boost through multiple brake applications is very important. We think that many drivers, faced with a growing emergency, are likely to try the brake pedal more than once before committing to a panic stop. That would be especially true on an open highway where instinct tells you to look for a place to pull over. Without brake override, that decision could be catastrophic.
What we did
We ran tests at our track to demonstrate what works and what doesn't if you ever need to stop a car with a stuck gas pedal. Note that despite the media attention it's gotten lately, unintended accerlation is a very rare occurrence in real life.
For our tests and video demonstration, we used two Toyota sedans in our test fleet, the Avalon and Camry. (Learn about how we test cars.) The Avalon is scheduled for recall work that will retrofit it with brake-override technology, and the Camry has already had that work done. So these tests show how well Toyota's brake-override system works.
Barely effective: One hard push
Driving the Avalon down our track with the accelerator floored, our driver reached 60 mph and then pushed the brake pedal to the floor and kept it there with all the force he could muster. The Avalon finally ground to a halt, after over 500 feet. A normal stop from 60 mph would take about 140 feet.
What not to do: Repeated braking
Again driving the Avalon with the accelerator floored, our driver found that applying the brakes more than once essentially eliminated the power assist. Using all his weight on the brake pedal was insufficient to stop the vehicle. The best our driver could do was to keep the Avalon from accelerating faster than it was already going.
What you should do: Shift to Neutral
If you're ever in a car that accelerates out of control, shift the gear selector to Neutral. Then brake to a stop. Even if the engine is racing there should be enough reserve vacuum power to stop the car easily. If you've depleted the vacuum you can still stop, so long as you're in Neutral and the engine isn't pulling against the brakes.
Brake override: Less thought, better choice
Driving our Camry with its newly retrofitted brake-override system, our driver reached 60 mph and applied the brakes while keeping the accelerator floored. The brakes immediately cut engine power, letting the car stop almost as easily as if the engine had been idling. Our driver also tried pumping the brakes a few times while slowing down, and that worked too. Each press on the brake pedal would slow the engine, which then allowed engine vacuum to recharge the brake booster.
Brake override: a treatment, not a cure
Brake override technology is so compelling that we think it should be standard in all cars. In our recent call forchanges to strengthen U.S. car-safety net, we recommended that the National Highway Traffic Safety Administration (NHTSA) require cars to be able to stop within a reasonable distance, even with the throttle fully open. While Toyota has pledged to make it standard on all future production starting with 2011 models, we wonder why they haven't done so earlier.
This brake technology should reduce to near zero the problems caused by stuck or entrapped gas pedals. But it's still conceivable that some electronic glitch could override the override. And no obvious fix will help people who think they are braking when they are actually on the accelerator.
Be sure to follow Consumer Reports Cars blog (RSS) and Twitter (@CRcars) to keep up with the latest information and advice, also see our unintended acceleration guide.
