ABS + energy recuperation braking would most likely always give a different fealing than regular power assisted brakes.

Electronic could certainly reduce the perceived difference.

Having driven a my 2001 Prius for more than nine years and having rented a 2007 and 2010 model, I can attest to the refinements of the second and third generation braking experience over that of the first generation models.

All, however, can demonstrate some disturbing characteristics, in varying degrees, to an inexperienced driver:

Encountering a pot hole, while braking hard, can induce a heart-stopping feeling of brake loss . . . like sliding on ice for 1/2 second . . . before the brakes regain their composure.

When braking hard, as one of the front wheels enters the pot hole, it becomes airborne, unloaded and hence the wheel stops rotating -- it locks up. The anti-lock braking system detects the locked up wheel and disengages regenerative braking. Since more than 70% of the braking force is provided by regenerative braking and its used by both front wheels, the system takes away more than half of the braking effort until the wheel encounters pavement and starts turning again. Once the ABS is satisfied the wheel is turning reliably, it re-engages regenerative braking -- restoring all the braking force that was in play before the pot hole was encountered.

Experienced Prius drivers, well aware of this potential, are on the lookout for pot holes while braking. We either coast past them before applying the brakes or we brace for the sickly brake-loss experience, knowing its a temporary condition and brake normally.

Thanks, storky, for sharing your experience.
I have no such experience in my 2007 Prius, however, I hardly ever brake hard, as that defeats the purpose of regenerative braking. I always brake very gently but well in advance in order to avoid friction braking altogether.

I am a believer in simplicity, and think that the owners should have an option to disable the ABS and the VSC (Vehicle Stability Control) altogether. I learned to drive in the days when cars are bone simple, with carburetor and breaker-point ignition...and did have a few scary moments while driving in the ice, but was able to quickly regain control. All modern drivers now should do some driving simulation in computer simulators in all types of road conditions in simulated cars without ABS and VSC in order to learn the true art of driving. Those who are certified to be able to handle icy roads and other road conditions in the simulator may feel the confidence to disable the ABS and the VSC in order to simplify work loads for the car's computer and avoid disaster.
There will be no electronic substitution for a well-trained driver.

Roger,

As the graphic accompanying this article demonstrates, only panic stops on the 2nd Generation Prius are supplemented in any significant way by hydraulic brakes. National Renewable Energy Laboratory testing in 2002 established that, short of a panic stop, energy recovery is not affected by the rate of deceleration. Whether heavy of light on the brake pedal, you recover the same amount of energy over the same change in velocity.

I have experienced MAJOR loss of braking in trucks & SUVs due to descending on unpaved, very rough mountain roads ( more than once) and, on one occasion a faulty rear axel speed sensor.
On other occasions (towing, rough roads etc) braking seemed to be mostly gone but no sudden loss was evident.

I expect the regeneration braking adds some complexity to the process (and some unsettling driver feel) but ABS still brings benefits that are (judged) well worthwhile.

Of course we cannot possibly allow any slight irregularities during everyday braking.

At present, perfection is lacking and I am surprised lawsuits are (thankfully) not inundating auto makers.

But this may be because ABS faults, on autos with little or no regeneration, might not be as easily detected.

Our ability to judge stopping distances does not really kick in until deceleration is established; then, and only then, we know for sure whether or not we will rear end that car ahead.

They will work this out - maybe accept more wheel lockup or (sob) less regeneration.

Storky: The graphic is correct, and is from a 2004 Toyota technical report on THS II.

1998-2000 and 2001-2003 iterations of the Prius used different versions of a powertrain that Toyota labeled Toyota Hybrid System (THS). The 2004-2009 Prius used a redesigned powertrain that Toyota simultaneously referred to as THS II and Hybrid Synergy Drive (HSD).

However, the THS II name fell into disuse, and Hybrid Synergy Drive remains the marketing term of choice for the company.

To put Toyota's issues in perspective:

--The braking problem in 2010 Prius is very minor and can be easily fixed with software update. Drivers should be reminded to brake gently and well in advance in any HEV, and not rely too much on anything man-made mechanical or electrical or otherwise. Drivers should also be reminded to use the parking brake and engine braking function upon failure of the main brake instead of panic, because brake failure could happen in any makes of cars.

--The acceleration problems in other Toyotas are very rare, like one in a million. Likely some faulty chips beside the "sticky" gas pedal issue. All the drivers need to do is simply shift the vehicle in neutral should the car starts to accelerate uncontrollably, and catastrophy can be averted. With our increasing dependence on micro chips, these one in a million failures will be quite inevitable. These type of malfunction could happen in other makes of cars as well, so the drivers should be taught to be mentally ready to shift to neutral and not to panic, and never be complacent that these thing cannot happen to other makes of cars.

--Future HEV's should have a mechanical shift lever to disconnect the engine from the drive train in case of computer malfunction.

--With respect to the 40,000+ traffic fatalities yearly in the USA, those handful number of people who died from allege malfunction from Toyotas represent an extremely minute percentage, the rest died from drivers' human errors. Should there be a complete recall of all human drivers? Short of that, should we have a stronger campaign to train better drivers? (instead of dependent on ABS, VSC, etc.)