Two-footed driving - safety issues

Factual Questions
41

There were a bunch of cases in the 1990s and early 2000s in which owners alleged that Ford’s cruise control was causing their cars to accelerate uncontrollably. Ford argued that its brakes could be used to overpower the engine such cases. Ford demonstrated this in a video that it used as evidence in many of those cases. I found this example of how Ford’s demonstration worked in an NBC news report about unintended acceleration.

Ford said it took 20 pounds of brake pedal pressure to stop the car. Note that the test begins with the car stopped and the car barely moving before the test driver applies the brakes. That is, the brakes don’t have to overcome any meaningful amount of inertia. I’m guessing that Ford used a car with brand new brakes and rotors. Thus, Ford is seems to be testing the brakes under the ideal circumstances to demonstrate whether the brakes will ever outpower the engine at wide open throttle. So yes, there are some circumstances when brakes on this particular car could outpower the engine.

But, consider if the car had been travelling at 50 mph and then opened to wide open throttle; the stopping distance would have been remarkably longer.

More importantly, video editing was Ford’s friend with this defense. Ford’s video did not include audio of the car’s test driver. After this test, the test driver reported the amount of force he applied against the brake pedal to stop the car (presumably based on a gauge measuring force at the pedal). At wide open throttle, the test driver reported pedal force at 175 pounds to stop the car.

Many drivers could not generate that amount of force. The amount of force required is probably increased in large measure because, at wide open throttle, engine vacuum is reduced and the power brake boosters are less effective. The mostly-elderly people who were major buyers of the Ford Crown Victorias and Mercury Grand Marquis that were having the problem would probably never be able to generate the kind of force necessary to stop the car under those conditions.

But, it gets worse in the real world. Stopping the car required the test driver to apply that amount of force almost instantly after moving off the line and when the car is barely moving (at maybe 5 mph?). Had the car already been at normal highway speeds, the test driver would have had to overcome all the cars inertia and the force of the engine simultaneously. This extended max-force brake application probably would have overheated the brakes, boiled the brake fluid, and caused complete brake failure while the car is still at wide open throttle. So, in the real world, brakes alone were not going to be enough to stop that car safely if, while moving at ordinary highway speeds, the car went to wide open throttle unexpectedly.

Brakes have gotten better over the years but cars have also gotten heavier and engines have gotten more powerful. I’m not sure how much better today’s cars would be at stopping under those same conditions.

42

Well, but the wide open throttle thing can be fixed using a thing called “N”. I use it a lot when slowing down and keep my AT in neutral at stoplights, to relieve the stress of trying to hold the car back.

43

Or you can get a Toyota newer than 2008, they cut engine power if you use the brakes. Umm, you know, after they settled with the government for over a billion dollars and killed a bunch of people.

44

It’s definitely hard on your brakes and does result in more frequent brake work if nothing else.

45

seems to me that you need your left foot to push against something like the floor of the car in order to brace yourself and lift your right foot for switching between the two pedals.

46

In my own case I had to with a car I had that would stall out if I didn’t use the gas a bit while at a stop. After some time at it I found it faster to apply brakes when needed then the one foot method. I have never accidentally stepped on the gas instead of the brake with 2 foot driving (and never the other way around either), however I have done it 2x with one foot driving which is quite scary. I believe one would be less likely to do so with 2 foot driving as each foot is for a independant control. With one foot driving one might assume one is on the correct peddle when they are not and keep trying harder if results are not as they expect. Also during normal driving situations my brake foot would be off to the side and it would only come into play when I expect braking, or if the situation was sketchy and I might have to brake which was not in contact with the peddle till needed, thus no chance of turning on the brake lights till braking.

All and all I find it can be more responsive but also as one does not need to drive 2 footed one (myself) over time re-defaults to one foot, and might be just simpler to teach that one foot is better as a all in one solution as I’m sure many would just do what is easier.

47

Was just reading a review of the Tesla model 3. It seems that the pedals work a bit differently than expected. The accelerator pedal can be set to a mode where releasing it causes the car to decelerate by using regenerative braking to charge the battery. The brake pedal works in the traditional way, using brake pads, so the battery is not recharged while braking.

I would think that if you drive a car configured like this, and are accustomed to using 2 feet, you aren’t going to get as much range, as you’ll be more likely to use the brake pedal for slowing than a person who is used to moving their foot to the brake pedal.

Incidentally, this seems to be different from many other BEVs where the brake pedal activates regenerative braking along with traditional brake pads.

48

I think this is another drawback, besides what I view as obvious safety issue, with using your left foot on the brake. Even in a internal combustion engine car you should be adjusting speed as much as possible with the accelerator not the brake. And depending on the transmission and mode setting some IC cars do that very well. Plus, some also have regenerative braking which activates when you let fully off the accelerator.

For example both are true in my BMW 328. In ‘sport’ mode the transmission chooses relatively lower gears so you get substantial engine braking when you let up on the gas, a lot of ability to modulate speed without using the brakes in driving situations that call for it (whereas in ‘comfort’ mode less so, and ‘eco pro’ mode the transmission actually goes to neutral when you let up on the accelerator). And in sport and comfort modes you activate regenerative braking by fully letting off the accelerator (or by applying the conventional brakes), where the car’s alternator applies braking force by charging the battery for the start-stop system which turns off the engine when you come to a full stop (not always, but under various circumstances controlled by software).

Using your left foot to brake would I believe surely exacerbate the bad habit a lot of drivers have of adjusting speed with the brakes rather than anticipating the need to slow down a little further in advance and doing so by modulating the accelerator. Friction brakes are for emergency slowing and emergency or routine full stops (besides deliberately aggressive driving on a track or windy public road). They aren’t supposed to be used for routine downward adjustment of speed, but it’s obvious following a lot of drivers that’s what they use them for, even without the dangerous habit of left foot braking.

49

To a certain extent that is already a feature in modern cars - for example, my actual 3 series BMW uses its normal braking light when I’m braking in a regular traffic flow but flashes all red backlights if I do an emergency braking by stepping really hard and with my full body weight on the pedal (which astonishingly people are reluctant to do - do they think they could break the brake?).

50

Pardon?

I don’t know about you, but IME neither feet nor foot pedals work this way.

51

There are specific techniques for two-footed driving that at least were used in race or rallye cars. Nowadays they all have sequential gearboxes, i. e. those that don’t require a clutch so this technique might be obsolete, but I just don’t know.

When I had the chance to talk to a profesional race driver about how they go ahead with shifting gears, I got the following explanation which includes using both brake and accelerator at the same time. With the same foot, yes, but the principle is sound. Race drivers are keen on keeping the engine running at the correct revs where it has the highest output, also when going around corners so the right foot right side stays on the gas while the right foot left side presses the brake. Meanwhile, the left foot pushes the clutch to change gears for the acceleration out of the curve. Sounds like something that requires a bit of training.

52

You’re talking about heel-and-toeing. It’s a common advanced technique for manual drivers.

53

I drive a manual, and dislike automatics. I wold never consider using my left foot for braking, as I am accustomed to quickly shoving the pedal to the floor with it. In other words, pressing the clutch. I wonder what the rationale for two-footed braking is, given that you don’t accelerate and brake at the same time. And, unless you ride the pedal with your foot on it, it would take longer to get your left foot in position than the right foot, which is higher up due to the gas pedal.

Keeping your left foot on the brake pedal seems silly. I assume that it has the same effect as riding the clutch; the brakes are applied slightly and hence will wear faster.

For obvious reasons, you should not use two-footing if you switch between a manual and automatic, even occasionally. In general, you would have to unlearn the quick move of the right foot to the brake pedal. Since your instinct in an emergency is to press the pedal to the floor, then there is a risk that you press the gas pedal as well. Hardly what you want just at that time.

Last comment; somebody developed a combined brake / has pedal. You pres to brake, and roll your foot to change the gas setting. I’m told people get used to it quickly, but I have never seen it.

54

There is a factual answer: road cars are not set up for left foot braking. Rather, they are set up with the accelerator and brake offset to the right for right foot operation. There’s also the issue that the vast majority of drivers have right-foot-only muscle memory ingrained.

As a practical matter, it would be more effective to use the left foot for braking and the right foot for the accelerator (now that the manual gearbox is in its death throes, at least). There’s a reason go-karts and open-wheel racers are set up that way, of course. However, so long as road cars are not set up for it, left-foot braking will be dangerous.

F1 cars were all set up for right-foot braking until semi-auto gearboxes with paddle clutches became standard in the mid-990s. Mike Hakkinen famously swapped between left- and right-foot braking methods and even helped McLaren develop a double brake pedal system (albeit not to allow the use of either foot, but to vary brake operation). Martin Brundle’s F1 career never really got back on track after he broke his left ankle and was limited to right-foot braking.

55

I never noticed the first, but last part is definitely true. I took a course at BMW and one of the exercises is really hitting the brakes (we did in a 3 series). It’s hard to realize the tendency not to do that until you’ve tried for absolute max. They tell you to try to break off the pedal, and if you can they’ll fix it and give you the car (you use their cars) for free. At full braking it feels like you’d be catapulted through the windshield if not for seat belt. Took me a few times to do it absolutely to the max, immediately.

The racing aspects of that course also convinced me the advantage of a non manual and right foot only in bracing yourself with left foot on the ‘dead pedal’. I realize that could be different in a true race car with other restraint, and where the car is actually set up for left foot braking (as in pedal on the left) for the split second advantage of pushing down one foot rather than the other as opposed to shifting the right foot. But for any practical case I really doubt the safety and efficacy of left foot braking. I think as was said the factual answer is that left foot braking is not how you’re supposed to drive, as reflected in the set up of the car. You’re not supposed to use your left hand to shift in a left hand drive car of your right hand in a left hand drive car either. :slight_smile:

56

Pickup trucks/cars with bench seats, 3-4 on the tree and with a cuddly girl friend, left hand for all tree stuff, right leg pegged against her leg and left foot clutch & brake.

In my life all 16 year old boys were masters of this art. Bet I could still do it if motivated in a car/truck of the old days and I am 75. Bawahahaha

57

That sounds awkward, reaching across like that.

58

nm

59

That conclusion is based on a very limited analysis of the situation that did not include a complete analysis of Toyota’s systems. The real analysis of the software and hardware systems took about 20 months and was completed two years AFTER that article. NASA performed an abbreviated review of the Toyota software but did not have time for a complete review (and Toyota provided NASA false and critical information regarding EDAC which altered NASA analysis, see below).

A very experienced group of embedded systems and software experts did perform a thorough 20 month review and testing of the software and systems, and also a review of Toyota’s software development process. Many very significant problems were found including a “fail safe” system that was designed so poorly it could not be effective (whereas Toyota’s Prius fail safe systems were designed correctly according to the expert).

This is the expert testimony:

This is the expert team’s presentation which goes into the key details:

Regarding EDAC:
Toyota told NASA that the main and sub-cpu’s had memory protected by EDAC when in reality there was no EDAC on memory.
After reading the presentation, I’m left with the impression that their software and software dev processes are pretty much just like most of the business software code and processes I see daily, which is generally poor. For business apps it’s not that big of a deal if there is a problem with a transaction or screen or report, etc. But for devices where safety matters, the processes, design and testing really needs to be higher quality.

60

I’m interested to know more about your experience with what you’re calling heel-and-toe shifting, and your implication that it was a commonly used technique in ordinary driving at some time. I’m not doubting you, just interested, because I only know heel-toe braking as a race driving technique (see below) and I’m not sure if that’s what you’re referring to.

Here’s my explanationof heel-toe braking as it is done on the track, from a 2006 thread. IMHO, using it on the street is generally unnecessary with modern transmissions, and is just showing off. :smiley:

I suspect you may have conflated left-foot braking and heel-toe braking. In cars with clutch pedals, you would very rarely shift while in a corner, and as I describe above, heel-toe braking is done in preparation for entering a corner. There may very well be drivers who have used the right foot to modulate both throttle and braking in corners, and I’m interested in hearing about any that do, but using the left foot, as I’ll describe below, is much easier

IME, the main reason for left-foot braking on the race track is to control weight transfer. Whenever you press down or lift up on the accelerator, you are changing the balance of the car’s weight on its tires: accelerate (in a straight line) and weight is moved to the rear tires; lift up on the gas, or hit the brakes, and weight moves onto the front tires. Successful car handling on track is largely a matter of managing weight transfer: too much or too little weight on any tire can cause it to lose grip, leading to a skid or spin.

When you brake with your right foot, taking your foot off the gas will cause your nose to go down, and applying brake will further increase that forward weight transfer. If you do this in a turn, it can cause your outside front tire to lock up or your rear end to swing out. That’s why racers do nearly all of their braking (and downshifting) before entering a turn. In general, you don’t want to make any significant or sudden changes to steering, braking, or throttle while in a turn. The ideal is to set a steering angle at the entrance to the turn and hold it while accelerating at a more or less constant rate past the apex and to the exit.

But there are fast turns where you may want to modulate your speed slightly without lifting the throttle. That’s where left-foot braking can be useful. By maintaining throttle position and applying the brakes with the left foot, you can make fine speed adjustments with much less weight transfer. You would not use heel-toe in this circumstance, because you need finer control of both throttle and brakes than could be managed with half your foot on each pedal.

I first noticed NASCAR drivers doing left-foot braking and realized it could help me with several turns on the tracks I drove, so I started practicing while on the street and began using it occasionally on track. It definitely takes some practice to do well.

For ordinary drivers, off the track, I think the potential problems mentioned above – lightly resting the foot on the pedal and either activating the brake lights, at best, or wearing down the pads and overheating the brake fluid, at worst – are not worth the small potential benefits. If, like most people, you keep your left foot on the dead pedal when not actively using it, it will be too far away from the brake pedal in an emergency. And IMHO trying to keep it suspended over the pedal without touching it would be tiring, and you could easily end up resting your foot on the pedal without realizing it.

So not the hard evidence that the OP requested, just one more opinion and experience from a slightly different perspective.