Traction control & braking on extended bumpy stretches

Have this sometimes on bumpy gravel roads. My response is foot off then foot on, only harder, to skip the regen section of braking. You also had traction control kick in too, to automatically reduce skidding. I'm sure you would have stopped ok if it was a panic stop. It does feel odd though.

 

Start braking sooner!
What the car is telling you is some wheel has bounced enough to cause it to skid. This triggers anti-lock and/or traction control. The traction control light is used for anti-lock indication as well.
It IS disconcerting when it happens, but if you press hard on the brake pedal braking will resume as you bypass those systems.

 

Regen braking is used most often to recover power lost during deceleration, but it only uses the front wheels. The uneven surface is 'spotted' by the car and interpreted as a slippery conditions and the car switches over to your regular 4 wheel abs disc brakes.... the very brief moment where it switches from regen to regular brakes does feel odd, like a momentary loss of working brakes, but it is perfectly normal and understandable.

You can simply leave you foot on the brake pedal with the same force if you like and the system will take care of you just fine.

Early cars, including mine, had a software update to shorten the changeover time... used to be even more milliseconds before the switchover... and it startled a few people. Me too when I first hit a patch of bumpy pavement on an off ramp, it almost felt like the car sped up when the regen dropped out before it changed over to friction braking.

Roland

 

Welcome to the dark side of technology.

People have actually been killed by ABS or saved by an ABS failure. Why? ABS lengthens stopping distance, and if it kicks in during a crisis stop, God help you. Traction control has it's own shortcoming. Power to affected wheel cut off, and it essentially denies you what that wheel could be doing for you.

All the tech presumes the driver is an idiot with no real driving skills. A machine-controlled car would have little to none of it because it would always use 95% of the brakes all the time without messing up like people do. Unfortunately, those of us trained on how to use our brakes properly have to adapt to a system that presumes we don't know what we are doing.

Yeah, anticipate your stopping situation...except you don't always know what you have until you're there. As a motorcyclist, I can attest that road awareness doesn't come through 100% of the time. Sometime, you just don't know what you're getting into until you are on top of it.

 

To stop the car, press the brake pedal. To stop the car faster, press the brake pedal harder.

It will in general sacrifice some amount of stopping power to ensure that you retain control over the car - the wheels don't skid, and steering ability is retained so you travel in the desired direction. So even if you can't stop in time, you might still be able to steer around the obstacle - and at the very least, you won't be doing circles into oncoming traffic. In general, with ABS and other similar systems, the best suggestion is to apply firm, constant pressure to the brake pedal, and the car will give you whatever it can without rolling you or sending you into other lanes.

To anybody who has spent a lot of time driving in snow, some of the feelings you might have had would be very familiar. Sometimes, you can just tell that you're about to get into an accident from 5 seconds away, but there's not a darn thing you can do about it because the car and the road just won't stick to each other.

 

This is a serious safety issue and should be reported to the NHTSA. Our Fusion Hybrid never behaves this way and there is no delay in shifting from regen braking to friction braking when engaging the ABS system.

 

Well, I wouldn't "brake hard" every time just because the system -may- cause a slight delay. The delay is around half a second. Just drive it like it's a hybrid with regen braking and you'll be fine. Anyway, when I have to brake hard I'm not concerned about what's in front of me, rather, the way people drive around here I check to make sure the moron -behind- me is paying attention!

As for the comment that ABS systems -lengthen- braking distances, it's just not true. They shorten braking distances at all times! Not even professional race car drivers can stop quicker. Proof of that is ABS use in race cars, and subsequent regulation of it by racing bodies (it's an unfair advantage)!

 

I certainly have and there is no way to deal with it simply because you do not know when it is going to happen. Sure, you should compensate for that by giving yourself some distance behind the car in front of you at all times but I live in the Chicago area and how am I going to do that? Very simple, I can not. It is a Prius problem with no answer to it. I just traded my Prius in for a new Avalon, not because of that problem. The Prius is a great car. I just wanted a luxury car. My Avalon is a hybrid and it has not so far had the braking problem "lunge" of the Prius.

 

It's not a safety issue, it's a perception issue.

 

Aye, the perception of my safety when going over bumps and applying the brakes only to continue unabated, is compromised

 

That was my original assumption a few years back, until I looked it up following somebody else's assertion that ABS could lengthen braking distances. Here's the straight dope, right from the NHTSA website (with added emphasis):

Do cars with ABS stop more quickly than cars without?
ABS is designed to help the driver maintain control of the vehicle during emergency braking situations, not make the car stop more quickly. ABS may shorten stopping distances on wet or slippery roads and many systems will shorten stopping distances on dry roads. On very soft surfaces, such as loose gravel or unpacked snow, an ABS system may actually lengthen stopping distances. In wet or slippery conditions, you should still make sure you drive carefully, always keep a safe distance behind the vehicle in front of you, and maintain a speed consistent with the road conditions.​

 

More so, if you know how to do "threshold braking," you can use 100% of the car's stopping ability. ABS won't let you do that because it's designed to kick in just before you reach that point. For a poorly-skilled driver, it's an improvement. For a skilled driver, it's a crutch they have to compensate for.

 

I have a 2011 Prius and have now experienced the "momentary loss of braking" effect which appears to be a characteristic of owning a Prius. I have owned many cars with ABS, and it usually kicks in when you are going too fast and braking too late for the surface you are on. Living in Ireland you get used to bumpy roads. What I'm not used to is having a car that's not comfortable braking on them......especially on an approach to a junction. On a normal car with a normal brake system going over a bump (or drop in the road) won't be enough to kick in an ABS, on a Prius this switch over and "loss of deceleration" is quite a thrill! I will have to start canvasing the local council to ensure all approaches to junctions are nicely smoothed out!

 

Let me preface my response to this older thread by first stating:

I love my Prius.

Having said that?

I have experienced in less than 2 years ownership almost the exact same situation as the OP, and it caused me to be involved in minor slow speed rear end collision. Not much damage but a PIA to deal with...

In my opinion, the Prius traction control system is overly aggressive. And also in my opinion it's a symptom of the entire system and how it reacts in a very specific, but also- very possible braking scenario.

If you happen to brake, on a man hole cover or simply a singular bumpy spot...you'll feel that perception of "lunge" or few seconds of loss of brake, this sensation I would say is pretty much the same sensation you would have with any modern car with ABS. Also in my opinion, no big deal.

The situation as described by the OP is slightly but significantly different. And that is if you find yourself braking on an extend length of bumpy or uneven surface that will kick in the traction control, over an extend distance or time frame.

Like the OP, my situation was I had plenty of braking distance between where I started braking and where I needed to stop, but had not taken into account an extended stretch of uneven pavement that existed because of recent road work and construction in that area. And like the OP the loss of braking power was not momentary but extended.

People that are saying "Just Brake Harder"....well no. Trust me, as the car came closer and closer to the car in front of me, the pressure I applied to the brakes went from "normal" un-panicked to my trying to press the pedal through the floor in an effort to get the vehicle to stop. I did NOT pump the brakes, but just applied consistent but increasing pressure as it became more and more evident the vehicle was not slowing quickly enough.

So I can attest to the reality that there are driving condition scenarios, that can cause The Prius to demonstrate a loss of extended braking power. This might be related in some ways to the singular slick spot or bump "sensation" reported, but is different, and IMO more dangerous.

I think the key is the length of the bumpy or uneven spot...combined with the kicking in and remaining kicked in...of the traction control system. In my opinion, if the traction control system thinks it needs to be active, and remain active, while you are braking through a longer patch of uneven surface, in an effort to keep the car "stable" and moving in a straight line, it can reduce your braking power as the traction control system works to allow wheels to spin to keep the vehicle moving in a straight line.

Personally? I'd rather deal with a skid, or a bit of fish tailing BUT stop in time. But the traction control is designed to avoid skids, and avoid spinning out or fish tailing.

If this is true why am I still owning and operating a Prius?

Because even though I personally think the traction control on a Prius is overly aggressive, especially when combined with ABS and regenerative braking (the complete system), I think the parameters of this situation very specific. And I think it's a situation where the traction control is trying to do the right thing.....keep the vehicle under control- even though it can inadvertently result in a scary or even dangerous situation.

Now that I know this is a possible characteristic of the whole braking/traction control system in unison? I think I can take responsibility for simply being aware that on an extended bumpy stretch of road or pavement, The Prius needs extra distance, as it is designed (on the positive side) to NOT skid, and/or not fish tail.

But can the scenario as described by the OP develop? Yes, I have experienced it.

Is it quite as simple as brake harder or sooner? No.

In evaluating the system as a whole, it is a trade off. While more primitive braking systems and vehicles without traction control, might allow you to skid and fish tail to a quicker stop without loss of braking power, you then have to deal with the risk and danger of skidding and fish tailing.

So I won't call this rare and specific scenario, and reaction a possible "flaw" but more simply the way the system CAN react. Something that as an owner operator of a Prius, I need to be aware.

No system in operation is entirely perfect. But in balance the times ABS and traction control are going to do good? Far outweigh those possible times they all work in concert to my detriment.

 

I assume that you have bought your Prius second-hand, otherwise you might have noticed this 'characteristic' before.
In which case being an early-ish car, do you know if the software update mentioned above, has been carried out?
If you are not sure, it might be worth while asking at your local Toyota dealer and see what their records say.

 

This happens to me with some regularity since I live in the NE with our lovely pot holed roads from the long winters. It is super sketchy. Seems like even if it is one small bump during braking you lose virtually all braking power for what feels like a very long time (probably less than a second). At times it feels like you'll never be able to stop on any road that is moderately bumpy. Luckily this hasn't happened to me in an emergency situation or caused me to get in an accident.

I second or third the sentiment about ABS and ESC being more dangerous and harder to control in many situations. The Prius' ABS is insane, I have never felt anything like it in any car I've ever driven. Out of all the cars I have owned I think my 5 spd 2003 Corolla w/o ABS or any traction control was probably the car that was easiest to control.

 

So much misinformation here...

ABS is designed to brake at the threshold of traction by oscillating on either side of that point. ABS is also designed to monitor this individually for each wheel on the car. So, ABS will brake the wheels independently up until the point where they start to lock up, then release slightly, and repeat. Modern ABS systems are able to do this upwards of 18 times per second at each wheel. What does this mean for you? If one wheel's threshold is different than the other three, the system can modulate just that one wheel, keeping the braking pressure at max for the other three. Unless you've four independent brake pedals (and the requisite four legs to operate them), you can't outperform an ABS system.

With one exception...

In deep snow or on loose gravel, allowing the wheels to lock will build up a wedge of material in front of each tire, allowing the vehicle to stop quicker. Having said that, the number of instances where someone is typically driving in such conditions is usually a fraction of a percent of the total time spent driving. Subsequently, ABS will be beneficial for the vast majority of the time.

Keep in mind, the main point of ABS isn't to stop you shorter (something everyone seems to think). It's to allow you to maintain control of the vehicle and steer around the obstacle in an emergency, as opposed to hitting it. It will also help keep you (along with the stability control), moving in a straight line, if so desired. If you're going to hit an obstacle, hitting it head-on is always preferable, as this allows the passive safety systems (air bags, crush zones, etc.) to function at their full potential.

As a friend of mine used to tell customers, "ABS stands for Always Brake and Steer".

Finally, no alphabet-soup of acronyms can repeal the laws of physics. If you exceed the limits of the prevailing conditions, you're going to put it in the ditch.

 

It is a big deal. It can cause an accident as you found out. And it does not happen with all cars that have ABS. I had a 2011 Prius Two for 3 years. It was terrible at lunging. I traded it in on a 2014 Avalon Hybrid XLE Touring. I have had it over 3 months and I have braked on manhole covers and bumpy roads and it has not lunged once.