Brake Failure (and an accident in a snowy day)

Why do you think that ?
Surface rust on rotors can and does occur after the vehicle gets about 10 miles on it.
Sometimes it causes absolutely no symptoms and no problem.
Sometimes it does.

You might be right.
I might be right too.

 

This rust is very strongly correlated to winter moisture and salt exposure, and also be to being parked unused for extended periods. My Subarus strongly fit this use pattern, I get to feel the brake pads breaking loose from the rotors, and I can see the rust outlines of the pads on the rotors. And of course the sound and different feel until the corrosion wears off.

The Prii get less salt exposure and shorter parked times, so show similar but lesser corrosion symptoms than the Subarus. But the reverse grabs on the 2010 felt very different, and didn't occur anywhere near salt season. The 2012 has had greater such exposures over twice as much ownership time and distance, and not done it.

 

Yeah I should respond: lack of brake modulation was definitely NOT rust related: often occurred at a second start up, after a drive, and in dry weather. Very much felt like something electronic malfunctioning: brakes either off, or locked, nothing in-between.

 

I had the exact accident almost 2 years ago. Snow on the ground, Came to a red line and tried coast to a stop, hit a bump and regen breaking changed to mechanical breaking, I floor the break. During that moment, car had completely no break. I reared ended the guy in front of me. It was slow speed, neither cars had any damage, but the guy filled for body injury(scam). Afterward, I called Toyota, they scheduled a special technician to check the car issue. Report said the car is normal, no issue found, case closed. After that I found the major issue with Prius is the breaking. Normally it uses regen breaking to stop the car, esp when you are soft on the break and coast to a stop. But whenever it hits bump, the regen breaking is lost and mechanical breaking kicks in. During that moment, car is out of break. Also tires makes a difference. But mostly just the stupid breaking system. Every time when it's wet or snow. I always keep farther distance. and keep an eye on any bump or metal surface like manhole cover. And most important if you feel it lost breaking, don't floor the break, just release and pump it a couple of time. But it's hard to react when it's in that emergency moment.

 

This means you were doing only light-to-moderate 2-wheel braking, not hard 4-wheel braking. Then you 'lost' the brakes for at most 6 tenths of a second before getting 4-wheel ABS braking. If this was enough to hit the car in front, then you didn't move to 4-wheel braking soon enough for the slippery conditions. You didn't leave enough space for winter conditions.

Key phrase here: "soft on the brake and coast to a stop". With less than ideal tires on less than ideal traction conditions (snow, ice, wet), you need extra stopping distance in any car, Prius or not. You must use harder braking, starting farther away. Allow far more braking distance in winter conditions.

This is required with all cars, not just Prii.

WARNING!! IGNORE THIS POSTER'S ADVICE, THIS IS THE WRONG WAY TO USE ABS! Using his advice may well cause a collision with the car in front.

With ABS, STOMP AND STEER! Pump-and-release is how to use old fashioned non-ABS when tires start to slide, but that method requires lots of extra space, like we used to do in the old days of winter driving. ABS makes that old pumping advice mostly obsolete, but we must still allow much extra distance.

Driver freeze-up is certainly a common problem in emergency situations. That is why the Brake Assist has been added to many cars, to apply full braking power when the car believes the driver intends it, but many drivers don't actually press hard enough. But pump-and-release may defeat this. With ABS, stomp hard on the brake whenever anything like this happens.

 

Any time ABS kicks in it does not give you more braking, it takes braking away. Cars without ABS can have shorter stopping distances in snow conditions.

 

Seems logical but it doesn't work out that way.
Way back when ABS first came out, a lot of "professional" drivers said exactly what you just did; that they are skilled and experienced enough to do it better the "old" way.

Tests were run with those "expert" drivers.
The ABS won in something like 80% of the tests.
And with "non-expert" drivers, the ABS won 100% of the tests.

You can believe whatever you want but that does not make it true.

 

In most slippery (wet, ice, snow) conditions, ABS will achieve shorter stopping distances than most drivers can without it. Experts who are good had threshold braking can do better still in some conditions, but that isn't most drivers. Nor me in most conditions.

There are conditions where ABS isn't as good, but those are mostly corner cases.

 

This is absolutely correct. I saw it myself when I bought my first ABS car and compared to a non-ABS car during winter conditions. when wheels lock in deep snow, they start pushing snow and the snow dam in front of wheel stops the car very effectively. ABS allows for wheels to roll on top of snow with little traction. This is very easy to test for anyone who wants to. People denying it simply never tested that and just ignorantly repeat what they think should happen. Now, this is about deep snow only, it will not work on ice or slush.

challenge for fuzzu1 and other ABS vs snow deniers: show us your evidence ABS stops better in deep snow.

note: I'm not saying ABS is bad, it's good and it allows for steering in all conditions, but lets just talk facts here and not just fake news.

 

We should note that people rear-ending the cars in front of them at intersections, are not driving in deep unpacked snow. Instead, they are driving on packed, compressed snow or ice, so this particular corner case is not applicable to the collisions described in this thread.

I'm not taking such a challenge on a claim I never made.

 

ABS came from the aviation industry except on aircraft it was called Anti-Skid. Can you imagine what would happen to an airplane if the pilot landed and the wheels didn't turn.

 

Yes. The resulting skid increases total stopping distance which makes a runway overrun more likely, and decreases directional stability, which can lead to going off sideways and clipping the runway wights. Lockup on dry pavement wears that spot on the tire abnormally and can cause a blowout resulting in total loss of braking or steering effectiveness for that particular wheel.
Relevant to OP, aircraft have published increased landing distances for wet or “contaminated” runways in the operating manual. If the runway is wet and the contaminated runway distance specified in the manual exceeds the length of the planned runway, the landing must not be executed and an alternative runway selected.
It would be nice to have those tables for each automobile model, but contamination like ice , snow, or slush has somewhat unpredictable effects on stopping distances depending on the exact ambient temperature and depth of the contamination. I would recommend practicing these stops with one’s own vehicle in different contamination conditions in a safe environment.

 

this is the one thing I want in an automotive HUD: show me a speed-and-traction-informed dynamic impact bar. More importantly, show it to everyone. Make it so all it does is suggest a line to put just behind the next guy's bumper. Driving on ice, it would recede much further ahead.

 

Maybe for a very skillful pro driver they can do better without ABS, for the rest of us: the "outcomes" are more'n likely better with ABS?

 

This has to have been studied. These recent posts, on both sides of the question, seem filled with "tests were run" / "believe whatever you want but" / "very easy to test" / "people denying it simply never tested" kinds of posturing, and no citations.

That can't be because no relevant studies exist. Granted, I haven't searched any up myself either, or I'd link to them here, but the first person who has the time to do that will be doing a service by steering the thread away from pissing-contest into more interesting directions....

-Chap

 

Pretty much. Andrew Day writes in Braking of Road Vehicles (2014): “The operation of ABS in cyclically releasing and reapplying brake actuation pressure may cause the time-averaged braking force developed at the road surface to be reduced below the maximum that might otherwise be achievable by a skilled driver. But usually, under conditions of braking where wheel lock may occur, such as emergency braking or braking on low adhesion road surfaces (wet or icy), a road vehicle fitted with ABS will achieve shorter stopping distances than the same vehicle without ABS, because the braking forces at each wheel utilise the maximum tyre/road adhesion coefficient rather than the lower sliding coefficient of friction between the tyre and the road when the wheel is locked and skidding” (p. 387).

From the Bosch Automotive Handbook (9th ed., 2014): “In general, [antilock braking systems] also shorten braking distances compared with braking scenarios when the wheels lock completely. This is particularly the case on wet roads. The reduction in braking distance may be 10% or several times this figure, depending on how wet the conditions are and the road/tire friction coefficient. Under certain, very specific road-surface conditions, braking distances may be longer, but the vehicle still retains vehicle stability and steerability” (p. 964).

What are those conditions? Toyota explains in their ABS & Traction Control System training manual (2002): “On rough roads, or on gravel or snow-covered roads, operation of the ABS may result in a longer stopping distance than for vehicles not fitted with an ABS.” (A similar caution appears in the owner’s manuals, by the way.)

Indeed. I’d probably start with the bibliography in the Automatic Brake Control chapter of the third edition of Rudolf Limpert’s Brake Design and Safety (SAE, 2011), or with the rulemaking histories of FMVSS No. 126 (requiring electronic stability control) and FMVSS No. 135, S5.3.2 (prohibiting controls to disable ABS).

 

@Elektroingenieur, I think you should get an avatar:

 

Auto from Wall E.

 

I think of ABS this way.... it's not necessarily saying it can stop you sooner... it's saying that you won't lock up and lose steering while braking hard. While related, these are 2 very different goals that (hopefully) produce the best outcome for the average driver.

My son is on the cusp of getting his drivers license, and we talk about, and test, all these scenarios regularly. He knows what it feels like when they Prius gets that hiccup between regen and friction braking—and what to do about it (stay hard on the brake, don't flinch). He knows, and practices, increased following distances in poor weather. He knows what it feels like leaving our neighborhood, which is downhill to a stop sign, when it's slippery and ABS is kicking around (in both our cars).

Practice practice practice. These are all normal things for new divers to learn, test, and practice. Most of us old farts tend to stop practicing and just rely on our old skill sets. Fact is, everyone needs a reminder and refresher, especially as auto technologies evolve.

 

I wonder what algorithms they are going to use in self driving cars on icy roads in the future...
I wonder if you can use radar to sense water on the roads or something like that.