Do your brakes, in addition to stopping the wheel rotation, also drive pylons into the ground to keep your wheels planted at the exact spot they stopped on?

If you keep your brakes on, the acceleration at the beginning and end of the car's movement will increase significantly, as the wheels overcome and then get overcome by the static friction of the rubber on the road. If your wheels can rotate, as soon as the impacting car touches you, your car will start accelerating, and assuming that you don't slam on the brakes after impact, the stopping acceleration will be no more than what you normally experience.

Actually, that's a good analog. You currently have the ability to stop your car fairly fast or fairly slowly. Do you stop your car as quickly as you can? If not, why not? Is it because it puts more strain on your body?

Keep in mind that directly following the accident the driver may be incapacitated. The car may roll if the parking brake is not applied.
I think this is the only reason to justify the rule.

There is no added benefit *during* the accident.

I'm with Doug on this one.

No brakes == quicker acceleration when hit from behind == whiplash.

Brakes == slower acceleration when hit from behind == slightly less chance of whiplash.

-ml

Has nobody here ever played pool?

Freeze two pool balls together. If you hit the first (car) correctly it stays where it is and the second (you) takes off, no brakes involved at all.

In reality the car and you have very different masses, and responses to the momentum imparted. The only way not to get hurt is not to get hit.

No brakes == quicker acceleration when hit from behind == your body is moving with the vehicle and your head stays safely against the headrest for a longer period of time while the energy of the striking vehicle is absorbed by pushing your vehicle.

Brakes == slower acceleration when hit from behind == your head presses against the headrest for a brief second then the energy is transferred to your body and your head whips forward and you get extreme whiplash or eat the steering wheel.

Good luck with your reasoning, but I'm taking my foot off the brake and probably even hitting the gas. Why don't you just whip that sucker into reverse and put the pedal down so you can have even less chance of whiplash?

Might the whiplash occur not when you accelerate, but when you suddenly decelerate when hitting the car in front of you?

My point exactly. Whiplash shouldn't caused by acceleration (unless you're moving in the wrong direction). It's generally caused by sudden deceleration, causing the head to whip forward.

If there's a car directly in front of you, it probably doesn't matter what you do either way.

Funny, because I always thought whiplash occurred when the vehicle moved quickly forward, moving parts of you with it and leaving other parts (your head) behind.

I've been at the front of a 4-car sequential collision. It would have been 5 or six had I not left enough space in front of me to the next car, unlike the douche bags behind me.

No. Whiplash is caused by sudden forward acceleration. Your body accelerates, but your head doesn't, your neck muscles can't absorb the strain and your neck vertebrae don't bend that way. Acceleration in the other direction is less troublesome because your neck is designed to bend in the direction that your head moves in that circumstance, the motion being stopped when your chin hits your chest. Maybe you'll break your jaw, but your neck will remain undamaged. And, if your brakes are on, your car will be going slower when it hits the [hypothetical] car in front of you, thus reducing the impact.

But that's all irrelevant in any case. The original question was is it better to use the brakes or not. I'll try to make it really simple here.

The more brakes you have on at the time of impact, the less the car will move. The less the car moves, the less you move. The less you move, the less damage you will sustain.

It's A, B, C. Simple (very simple) Newtonian physics.

tanstaafl.

Damn, Doug. How's your neck? I mean, you moved all the way from Alaska to Mexico. It's amazing your head is still attached.

I don't know the answer, but it seems to me that there's an easy test for this: in collisions where a moving car has rear-ended a stationary one, do the occupants of the moving car ever get whiplash? If so, large negative accelerations can cause it (and thus you should ease off the brakes); if not, only large positive accelerations can cause it (and thus you should keep them jammed-on).

Peter

Only to Americans - this is how we drive in the UK. Use the handbrake when stopped in traffic where there is any slight incline, at junctions and traffic lights. It is as taught this way with IAM (Institute of Advanced Motorists) and Police driver training too (friends who drive police cars both use the handbrake - and their training is strict). It is just a better method, there is no advantage of not using the handbrake in this way apart from less effort and not appearing a newb to Americans.

SWMBO frequently asserts that it isn't!

tanstaafl.

Not only to americans...

In my opinion, it would take longer to get moving if you use the handbrake than using just the regular brakes. What about owners of the new Passat, what do they do? The new Passat doesn't have a normal handbrake, but an electro-mechanical brake operated by a switch. I know it will release if you have the seat belt fastened and you depress the accelerator (don't know about manual transmission, I have DSG transmission), but I would guess that would wear it out fairly quickly

Stig.

America doesn't make up the whole rest of the world. I think what you're describing is perfectly valid, but it might be a UK-specific thing, or otherwise limited to the UK and a number of other countries. But it's not universal minus America. Besides, in America, I don't think anyone learns how to drive in a manual car. I'd be interested in finding out what percentage of drivers (in Canada and the US) even know how to drive manual, but I'm guessing it's probably below 25%.

Yeah, its easy to think so, but its not the case. I'm doing the same thing with my feet as you, just releasing the handbrake with my left hand at the same time. It all happens concurrently, so its not slower at all. In fact, it makes it easy to dial in a few revs before I let the clutch up (and drop the handbrake at the same time) if I want to move quickly. You can only do things like that on a completely flat road if you don't handbrake.


Hmm, yeah those are all Auto's or DSG type cars though. When you lift off the brake they must engage drive so you can't roll backwards (they probably creep forwards too, right?). That way you are not ever freewheeling when you get off the brake like you would be in a manual car with the clutch down (or out of gear). So the control is always there and its okay to just use the foot brake.

You need to shift the car into 1st before you release the hand brake. That's two actions, though I suppose you could have the car already in first while stopped, sitting there holding down the clutch. When I'm stopped I'm not in gear.

No, but the occupants of the stationary vehicle do, 100% of the time. Or so lawyers and popular television would have us all believe.

No, you don't. If you let out the clutch slightly so it just starts to engage before you release the brake, you wouldn't slide back.



No, they're not. All the new Passats, automatic, DSG or manual transmission, have the same parking brake.

But, anyway, I think we just have to agree to disagree on this matter...

Stig

I was taught to use the handbrake and if I'm stopped for more than 10 seconds, I do. Sitting riding the clutch will only wear it out. Plus if you get hit from behind you're less likely to plough into the car in front.

Why would you be riding the clutch while stopped? You don't have to hold the clutch if you're in neutral. Where, IMO, you should be if you're stopped and not just about to launch. When you're coming to a stop you'll have to shift anyway, instead of putting it into first (which I've never heard of anyone doing while the car is moving), drop it in neutral and leave it there. Your foot brake will hold the car in place while you're stopped. When it's time to go, one fluid action should put you in gear, clutch and accelerate. Get used to it and your car won't even move an inch in the wrong direction.

I understand whiplash to be a sudden jerk of the head in a rearward direction, caused by a sudden forward acceleration of the body (supported by the seat) while the head was unsupported, hence the fitment of adjustable headrests in modern vehicles to restrict rearward motion of the head.

Re: shifting into 1st while moving
In 'not so modern' gearboxes where there are no synchros for 1st gear (and also for worn synchros) it can be difficult to get into gear if the car is stopped.

I agree with you, though. Just thought I'd drop that tid-bit.

I always found that when I couldn't get it into first while stopped that letting out the clutch pedal while in neutral usually helped. Of course, that probably has something to do with synchros, so probably irrelevant.

Ok here is my new reasoning as to why British stop lights go yellow both ways.

Early stop lights needed to be switched.

A simple 4 pole rotary switch driven by a clock motor could control an entire intersection's worth of lights. Connect the n/s red lights and the e/w green lights to the first pole, all yellow to the second, the e/w red and n/s green to the third, and all the yellow again to the forth.

It sort of fits the tech available when stop lights of this type were invented.

Except that they go: Red, Red+Amber, Green, Amber, ...

Speaking of light rotation, there's an intersection near me whose right-turn-only lane light does this:

1. Light is green (90 seconds)
2. Light turns yellow (8 seconds)
3. Light turns red (2 seconds)
4. Light turns to a green arrow (90 seconds)

(times approximate)

I can't tell you how many times I've arrived at that light and had to come to a complete stop, only to immediately go again, just because some schmo couldn't be bothered to program it reasonably.

If there actually are people driving left-to-right across the intersection, then it (obviously) stays red for longer. But that's relatively infrequent and people blow through the light all the time because it's just insane for the transition between "you can go" and "you can go" to be to come to a stop. So not only does this irritate the piss out of me, it's dangerous, too.

… although my name's not Bamber …

Definitely with Hussein on this. I have various police Roadcraft training and IAM, and the benefits to using the handbrake are as follows:

Reduction of whiplash injuries if your car is rear-ended as car will not accelerate as fast when hit
Reduction in knock-on collisons if your car is rear-ended
Reduction in accidents from drivers accidentally letting their foot slip off the brake pedal
Reduction in wear to the clutch as even when it is held in, there is incremental drag
Reduction in brake light glare for the driver in front
Shorter pull-away time, as your engine can be at optimum revs before releasing the brake
Less leg strain - long periods in stop go traffic where the left leg is always pressing the pedal result in reduced blood flow and in extreme cases can lead to or exacerbate DVT

There were others as well, but I can't remember them all. These ones make it obvious to me why using the handbrake is a positive benefit.

So, if the new American embassy was involved in a RTA should they apply the handbrake or not?