Brake Failure (and an accident in a snowy day)

Hi neighbor, I am sorry and feeling disturbed to hear about your experience. I urge you to report this incident at NHTSA | National Highway Traffic Safety Administration If just a few other people have something similar to report, the NHTSA can order a recall.

 

welcome!
probably some black ice or some such. do you have snows? try leaving more room between you and the car in front

 

I am sorry to hear about your accident, though glad to hear that the damage was minor and no one got hurt. From the description it doesn't sound like brake failure to me. I am not an expert, but as I understand it, what stops car is not a brake, but it is tire in contact with slippery surface of snow covered road. I your case, you had all season tires which was not capable of producing enough friction on snowy surface and you skidded. Driving on snow/ice takes certain level of skills, but good winter tires might have prevented this accident, IMHO. If you anticipate driving on snow again, you might look into getting dedicated snow tires.

 

First of all, ABS cannot overcome physics. Keeping your foot on the brakes, letting the ABS work as designed, is believed to be the best method. Don't know if this was the case, but slushy wet snow (melting snow on top of wet roads) creates an impossible stopping situation. Slush sticks to your tires and slides on the slush built up on the roads. Essentially ice on ice. You've got to have good tread depth on your tires. Dedicated snow tires help a lot. Practicing with your ABS in controlled situations lets you know how the car will behave in advance of a panic situation. Practice some panic stops in a wide open parking lot, for example, so you know how your car will behave.

 

Clue #1.

At this point, in real winter slippery conditions, you have already lost. Collision is inevitable even with working brakes and average wet traction.

I.e. worse than average wet traction, closer to very bad case slippery, which winter drivers need to be ready for.

How many miles on them? What is the remaining tread depth?

Based on my experience on how fast All-Season tires lose their initial winter ability, a significant portion of high mileage drivers have already turned them into just 3-season tires within a year. And they never even start out as good as true Winter tires.

Absent more details, we still lack enough information to sort out brake failure vs simple winter traction failure. In a previous car, I personally experienced slow slick winter conditions where all four wheels stopped turning simultaneously when brakes were applied, rendering ABS useless. (ABS works only when it detects a mismatch in wheel speeds, but 4 locked wheels are a perfect match.) Fortunately, I had 250 feet of clear street available to recover, not a too-close 15 feet.

 

I don't think the brakes failed.....but the driver did.
The "rule" for stopping with ABS is:
Stomp
Stay
Steer

It sounds like you didn't give the ABS a chance to work.
Pumping the brakes, like you should do without ABS, actually defeats the system.

I think EVERYBODY should practice skid control on ice in an empty parking lot so that they will know how the ABS feels and what it's limitations are. But almost nobody does.

 

this is one glaring weakness of ABS, stopping in snow is much worse than non-ABS cars that lock the wheels and snow pile builds in front of blocked wheels.
however, ABS gives freedom of steering and pulling to side was the correct solution.
but one has to practice emergency stops like that to be ready for the next time.

 

It won't take much to lock the wheels if you find a wet enough place, and go over the white parking space markers.
It will feel like you've hit a hole, or are riding the reflectors between lanes. Just make sure you're at the back of the
parking lot away from all the cars. You don't have to stomp on the brake pedal, just press hard and fast, like an
emergency stop and you'll feel it. It's a weird feeling!

 

Everyone misunderstands ABS.

ABS does not help you stop.

ABS actually worsens your overall stopping ability, by a small amount. However, it dramatically improves your ability to steer while brakes are at maximum.

If you don't choose to steer somewhere other than an accident site, or if there is no other place to choose, then it doesn't do any good.

Snow tires would have helped, but even they might not have been enough. I had to drive (other car) in the Philly area that day and I didn't have an easy time either- that was wet snow on top of polished ice. Just about the worst traction problem any car could ever face.

 

I have Michelin X-Ice tires for the winter. There was a day last year where it had mushy snow/rain. I was merging into the left-turn lane and braking/slowing down to make a left turn at a traffic light. The car suddenly went over the metal drain vent in the road. Yellow traction control light comes on and the car was slipping in the slush. I sliding towards the car leading for the left turn in the intersection! I pressed on the brake pedal as hard as I could. Luckily I was already going pretty slow. I managed to stop barely before the other car's bumper. I was sweating at that point.

The Prius's tires did not lockup despite pressing the pedal fully to the floor when the traction control comes on. It took about a half second before brakes engaged again. I agree, the Prius loses brake control after going over bumps and is dangerous.

I have tested my brakes before after each brake job. The ABS is supposed to lock the tires up if the driver presses the brake pedal to the floor.

 

...and then unlock them a fraction of a second later. That's the anti- part of anti-lock.

By keeping the wheels turning, you don't skid out of control. You won't stop as fast as you'd like, but at least you still get to pick which direction you go.

 

The "stomp" applies to panic stops.
In adverse conditions, wet or icy, when a crash is not imminent, pushing firmly on the pedal is better......because if the wheels don't lose traction the ABS never comes into play.

The key is when you hear that loud buzzing sound of the ABS working do NOT release the brake. The computer will do a better job of modulating the brakes than you can.

Then, the odds of you or the car being "damaged" are much higher if you do NOT practice panic stops somewhere when there are no other vehicles or buildings nearby.

 

What??? I thought when the driver slams on the brakes for an emergency stop ABS makes it so that the wheels of a car do not lock and slide. Am I missing something here?

 

Yes that was one crazy snow storm...caught everyone by suirprise.
I had a 9AM appt to replace the tires, so I tried to make it, had to turn back home, but I got most of the way there.
Anti lock brakes light was on all the time.
I saw lots of Prii out there, some fast. It was a strange situation with heavy snow, yet heavy traffic, many were trying to demonstrate how fast they could go, others were stranded on the side, so it was not good.
The old tires definitely seemed worse as expected.

Definitely we feel the brief brake loss on a bump, but brakes always came back after that.

 

Strongly support the “practice in a parking lot” idea, but emphasize that it should be a very BIG and EMPTY parking lot! You also want NO light posts or other solid obstacles in the part you use and should have a minimum of a football field of space. Fasten your seat belt securely without slack!
Wait for a day with limited traction conditions where the main streets are cleared but the pakring lot is still snow covered so you can safely drive over to practice. Start your practice stops way down at 10-15 mph and do the “stomp, stay, steer“ type of panic stop at that speed. Gradually increase the speed until you get to a speed where you can feel the ABS kick in, which gives an odd, very quick pulsing to the brake system which you can feel and possibly hear as “thuddah, thuddah, thuddah..”. But Knowing that feel and sound will help prevent you frim lifting your foot from the brake due to being surprised in a real panic stop. Also try steering while ABS is functioning because the steering is much sloppier than the crisp steering you get on dry pavement, and it is also limited because if you try to steer too sharply you can still induce a sideways skid.
As I understand it, that “bump-causing-brake-loss” comes from the bump causing the computer to cancel the regeneration part of the braking system. It feels like you momentarily totally lose the braking which is extremely disconcerting , but if you press to the floor you should still get the hydraulic brake system effect. But I need to practice that some more to see if all that works as I think it does.
One last idea: consider using the Emergency Brake if the normal braking fails? You should get a minimal amount of braking from the rear wheels, but it would be better than nothing and might make a crucial difference in a very low speed braking scenario.

 

Explanation: When rotors are wet and you slam the brakes, at times car will not slow down or stop. Water becomes a lubricant when an object in motion like 2,100 lbs is on rotors, weight & inertia will cause brake pads will slip. This has happen to me on all cars I've own, except a Prius because I drive like a grandpa for FE.

 

Yes. From this website, How to Use Anti-Lock Brakes | Freeway Insurance

How to use four-wheel anti-lock brake systems:

• Slam on the brakes. The ABS should stop the wheels from skidding.
• You may feel the brake pedal vibrate and hear a clicking sound – this is normal.
• DON’T pump the brakes (this will deactivate ABS).
• Keep your foot firmly pressing on the brake pedal.
• Keep steering to enable four-wheel ABS to work properly.

 

The improved steering certainly helps. But I clearly remember that during ABS's development, long before it was rolled out to the public, it was being sold as shortening braking distance in common wet road conditions. Yes, there are corner causes where it doesn't shorten the distance, but that isn't the wet road norm.

The principle is that threshold braking is stronger than sliding locked-wheel braking, but most drivers aren't good at it even without the complication of mismatched traction conditions under the various wheels. ABS does a usable approximation of threshold braking, and automatically adjusts for the variable wheel traction.

Agreed.

This shouldn't happen within the normal power-assist braking range, ABS's purpose is to prevent lockup. Any lockup should happen only when pressing so hard that it completely overrides the power assist system, such as when reverting to completely manual braking when the booster or control system has failed. (BTW, this manual override is a NHTSA requirement for passenger cars, meant as a fail-safe for boost or control system faults.)