Unintended-acceleration investigation continues

I've also done this test with my Prius at 40-ish mph and at WOT at 90+ mph and with my wife's Highlander at 50 mph in full traffic to show her what happens.

In the Prius:
PWR button OFF for 3+ sec, controlled slowdown
Shift to Neutral, ICE remains ON but there is a controlled slowdown
Shift to Reverse!!, ICE powers OFF with a controlled slowdown

Highlander:
Shift to Neutral with foot pressed to the floor, the vehicle revs wildly until it hits the rev limiter but immediately begins a slow coast to STOP. I re-engaged the transmission so as not to block the flow of traffic.

As regards the Santee accident, my own worthless and factless speculation is that the driver noticed the excessive speed due to the AW mats pressing on the gas pedal and he did the normal thing which is apply the brakes. All is good thus far.

But all modern vehicles have brake assist from the ICE. However when the brake pedal is released from the initial depressed position the vacuum assist is lost. The next pressing on the pedal has less power, the next pressing even less power, etc, etc. Pumping the brakes is absolutely wrong here. At that time the vehicle is going faster and faster and faster and all braking force is lost.

The only way to slow down was to dislodge the AW mat from on top of the gas pedal. The brakes would have been useless. That's true of every modern vehicle now days.

But this is only my own personal, worthless and factless speculation.

 

This^^^

This is something that I'm certain that 99+% of the drivers on the road know nothing about.

 

For most (not all) modern vehicles, this is where the driver has a choice to make. There is no single correct answer.

With the most common cause of these events, pedal misapplication / driver error, pumping the brakes is the (or a) right thing to do. It was sufficient to clear my event (though another action was also sufficient), and it provided strong evidence to the cause.

But with the mechanical fault in the Saylor incident, it was the wrong thing to do, as it reduced power boost and added heat to the brakes.

Because neither answer covers all situations, it is best to have some additional measures available.

That wasn't the only way, unless there were additional problems we don't know about. We don't know why he didn't shift to neutral (the single allegation I've heard of this becoming impossible under load has not been backed up). He could have shut off the ignition, but that car was substantially different than he was accustomed to, in a way that continues to confuse some drivers new to the system.

This brake failure mechanism is not true of every modern vehicle, only those using manifold vacuum to power the brake booster, which is most modern vehicles. The electric brake boost in Prius, FJ Cruiser, and who knows what else, should not suffer any loss of brake boost at WOT. And the throttle-brake override in some cars, starting with Audi after the hysteria of a quarter century ago and since spreading to many European (and Chrysler?) models, should also prevent most of this loss. Now Toyota is embracing it too.

 

Just watch those drag race RWD "spin outs" to preheat the tires before the actual race. Light brake application at WOT, rear drive wheels spinning wildly, but the vehicle remains pretty much stationary.

Try THAT with a FWD vehicle.

 

Umm you can do the same thing in a FWD vehicle as well. I'd been drag racing domestics from 1992 until 2005 when I bought my Prius and had plenty of track time under my belt. FWD cars can indeed perform burnouts like a RWD car can.

Fortunately this has nothing to do with being able to stop a vehicle stuck at WOT. Most street cars will stop with the application of the brakes, even the throttle by wire systems. In some cases a highly modified high HP vehicle could be difficult to slow down quickly but this would be rare case and the car has been extensively modified from stock so the point is moot.

Mine. (I slammed on the brakes before the end so I didn't get booted for lack of a 5 point harness). Ben thought I was on spray but I was definitely NA. lol

Theirs..

 

Yep, I stand corrected. He could also have shifted to Neutral or powered the vehicle OFF.

Yes since this horrific tragedy TM has installed the Brake Throttle Override in all its new models as part of its installed safety features, Smart Stop.

 

Apples vs Oranges...

FWD on a low traction gravel road vs.......

Still, I wouldn't have guessed an e-brake would be strong enough even though...

 

I'm sorry, you lost me. What does gravel road have to do with the topic? Have you never observed a FWD doing a massive burn out at a drag race track? If not then I'm not sure your experience and knowledge level qualifies you to argue this point.

I have both experienced (emphasis on owned and raced) very high powered street cars and their braking action and read about them. There is even a link in this very thread to a high horsepower Mustang and the stoing distance from 100mph-0mph at WOT.

Because some want to argue the ECU connection to the throttle is the reason the brakes can overcome the engine yet the same can occur in a direct linkage like that found in most older cars including muscle cars of the early 2000s.

 

On most cars, a properly adjusted e-brake will lock the rear wheels up on dry pavement. So the only problem is traction.

Still, there is more weight on the front wheels of a front wheel drive car than the rear. So, how do they keep the car from moving with the emergency brake on the light end and the engine spinning the front wheels on the heavier end of the car with more traction?

Easy, they usually "cheat". One way is hit the front wheels with a burst of power and get the front wheels spinning before the car moves very far. The spinning, smoking tires lose traction because the rubber is melting and the emergency brake continues to hold the car. Or, they can cheat by putting some lube (even water) under the front tires to get them spinning easier. Or, like in the video, they can do it on an upgrade and be rolling backwards when they hit the power.

 

I love that you know about racing.