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The question is in reference to cars.

A picture depicting the pedals in a car - L to R - Clutch, Break and Accelerator

The accelerator pedal is more elongated than the other two and usually softer as well. Why?

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There is no mechanical reason for it. You right foot spends most of its time on the gas pedal, so it's larger for ergonomic reasons. As for the soft/stiffness, that's a function of car maker's philosophy and tradition. A lot of German cars have floor-mounted gas pedals that are very stiff to operated, whereas many Japanese cars have ceiling mounted ones with much less resistance. –  Jung Lee Mar 22 '12 at 14:06
    
@chrisF is right, it would avoid much of confusion between acceleration and break pedal, especially for newbies and elderly!. Ofcourse pro's know how to step up the gas!! ;) –  sree Mar 22 '12 at 14:15
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IMO the better question is why the heck the clutch is often identical to the breaks... –  Ben Brocka Mar 22 '12 at 14:22
    
@ Jung Lee: some german cars have 3 floor mounted pedals (e.g. Porsche) –  Bart Gijssens Mar 22 '12 at 15:03
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3 Answers

up vote 8 down vote accepted

So you can tell which one you are pressing and to make sure it's harder to operate incorrectly.

It's designed so you can't accidentally operate the accelerator and brake pedals at the same time with a single foot. Pressing the break and accelerator at the same time is dangerous - both in terms of the damage you could do to the mechanics of the car and because you are likely to cause an accident. It's narrower so that it's hard (if not impossible) to catch it if you don't get your foot squarely on the brake pedal.

The shape and angle will make it difficult and uncomfortable to press with your right foot - even if you can reach that far.

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+1 Also, in automatic cars, you'll notice that the brake pedal has a much wider target area for the same reason -- faster to find and operate. This would simply be hard to accomplish with the clutch. (performance-car-guide.co.uk/images/pedals.jpg) –  msanford Mar 22 '12 at 14:12
    
Chris, careful with phrasings such as "right foot", since that varies by country. In the US for example the layout is such that it would be the left foot that has trouble pushing the accelerator. –  Kevin Cathcart Mar 22 '12 at 17:35
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There's no difference in the floor pedal layout between left-hand and right-hand drive cars! Accelerator and brake are always right-foot, clutch (when present) is always left-foot. –  Jim Mar 22 '12 at 18:44
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The brake has a shorter pull than the accelerator. There are usually only two things you want to do with a brake: slow down or STOP RIGHT NOW. There is a lot of variation with an accelerator and how people drive with it. For instance on long trips (when I'm not using cruise control) I rest my heel on the floorboard and use the tip of my toe/my ankle to control the accelerator (to help avoid fatigue and the adjustments are more subtle). When I'm more engaged in the driving, I will bring my foot up and use my upper leg to control acceleration. Here I'm making coarser movements (usually accelerating more aggressively). The length of the pedal accommodates both of those modes of driving.

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I nearly agree with this. I'd argue that longer lever action of the accelerator pedal allows the driver to use very small variations in force on the lever to signal very small changes in the setting of the 'power control' at the engine. It therefore enables more sensitive control. –  PhillipW Mar 22 '12 at 21:06
    
I think that's what I was saying...sorry if I wasn't clear. Using the ankle/tip of foot for fine grain control and full foot/hip for coarser "pedal to the metal" action. –  Mike Brown Mar 23 '12 at 2:01
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There are 2 reasons for this:

  1. Safety. If you need to make an emergency stop in a panic situation, the natural thing to do is to just step on the pedals with both of your feet. If the gas pedal is located "deeper" than the brake and clutch pedal, the gas pedal will not be pressed in in such a situation. The result is that both the clutch and brake pedals will be pressed in, which is exactly what you want.

  2. Ergonomics. Irrespective of the type of pedal (floor or ceiling mounted), the brake pedal is optimized for force and response. In order to achieve this you need to start pressing the pedal with the knee in an angle sharper than 90 degrees. The gas pedal is positioned in such a way that the foot can "rest" on the pedal. The angle of the kee is more or less 90 degrees. The pedal position and form is optimized in order to relax.

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I was explicitly taught not to use the left foot in an emergency stop (i.e. push the brakes without worrying about the clutch). Why would you want to operate the clutch pedal in such a situation? –  Gaël Laurans Mar 22 '12 at 20:49
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Because if you do not declutch, the motor will stall. If the motor stalls, I think you will loose power steering, power braking, ABS,... –  Bart Gijssens Mar 23 '12 at 6:42
    
Well, of course the motor will stall (and it obviously did when I exercised it) but will all this really matter in an emergency situation? How do you know? –  Gaël Laurans Mar 23 '12 at 23:51
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@GaëlLaurans: Envision the following situation: You're passing through an intersection at ~30MPH/50Km/H when you suddenly notice a child in the street ahead of you. You slam on the brakes, the child runs out of the way and your vehicle stalls when you come to a stop in the middle of the crossing. Then you glance to your left and see a bus coming straight at you, tires squealing as he tries to stop before hitting you. Had you instinctually pressed both pedals, you'd be able to accelerate away before being hit. –  Justin ᚅᚔᚈᚄᚒᚔ Oct 30 '12 at 17:59
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(continued) Also, engine braking does nothing to help braking in an emergency situation since you're already braking at the limit of the tires (either you're skidding or ABS is doing its job). The situation I described above has actually happened to me, and if I had not been taught to hit both clutch and brake then I could very easily be dead or disabled today. In an emergency, you want to have as much control over the vehicle as possible -- it could save your life or the life of someone around you. –  Justin ᚅᚔᚈᚄᚒᚔ Oct 30 '12 at 18:03
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