How to avoid rearend accident?

[napmatt]

yeah i agree, pumping the break lights is your best bet, but even then, brace for impact.

[Ms_Jam]

FgNewbie

The median strip is wide, but has a hard concrete edge.

Thinking about it now, I probably would have done some damage to the underside trying to mount it in a hurry. I have the 2-door version of the WS Fiesta, and with only 16 inch wheels and sideskirts, it sits lower on the road than the majority of other cars.

By the way, can I thank everyone who has offered answers to my dumb question?

I have learned a lot!

I never dreamed the thread would attract so many replies.

[aussie muscle]

Originally Posted by sudszy

Very poor advice in my opinion. Im more interested in minimising personal injury in such instances, money can fix broken cars but maybe not broken necks and backs.

If you keep your foot of the brake, the car can move forwards more easily in the impact, that means you in the car are accelerated forwards at a higher rate, increasing your risk of injury.

...,

this is all about energy dispersion. if you have your wheels locked hard, the energy will go through the other parts of the car. if the wheels are free, the energy can be transferred into motion of the stopped car. you should know hitting a solid immovable object is more painful than something softer, lighter or moving. my advise would be to put your head back onto the headrest so your neck is not snapped, but let off the brakes, and apply them after the impact to stop the car rolling into another car/intersection.

[geckoGT]

Originally Posted by aussie muscle

my advise would be to put your head back onto the headrest so your neck is not snapped, but let off the brakes, and apply them after the impact to stop the car rolling into another car/intersection.

You would have to have lightning fast reflexes to achieve that.

[LTDHO]

Originally Posted by aussie muscle

my advise would be to put your head back onto the headrest so your neck is not snapped, but let off the brakes, and apply them after the impact to stop the car rolling into another car/intersection.

Perfect advice, I do the same.

It's true, I'd rather the car be at a panel beater or wrecking yard than me in hospital or morgue!

[kypez]

Originally Posted by FgNewbie

Damo refers to free rolling, others suggest less or no brakes. Applying these principles, if someone smashes your rear at 30 kph, what distance is required between you and the car in front to avoid smashing their rear?

How long is a piece of string?! You can never really know because it depends on the car you are in, the type of vehicle that hit you, tyre condition, road surface, and so in and so forth.

[The Yeti]

Originally Posted by Ms_Jam

The bad news is that last night another car rearended me.

I was stationary, about three cars back from traffic lights, in the right lane with a median strip on my right. The lights had turned green, but the cars in front did not move. In my rearvision mirror, I could see a car coming up fast, too fast, behind me. I expected it to hit me, and in a couple of seconds it did.

My question of the wiser heads here is what could I have done to avoid the accident. My WS Fiesta Zetec has nice big tail lights, with a horizontal tail light on the spoiler. Would brighter bulbs have helped? The current ones I got from Repco (their in-house brand). Someone this morning suggested Narva lights.

Were the lights working correctly and as bright as OEM (repco house brand I suspect would be no different than Narva & OEM)

Originally Posted by Ms_Jam

Second, I could have slammed my car into first gear and tried to get onto the median strip. But I wonder whether I would have had time.

Lets say you did have time, and you footed it up on to the median strip, or out of that lane in to the flow of traffic, had you damaged your car and this other car had not hit you, you would be the one paying for the repairs to your car and any other damage you did, not the guy that now only nearly hit you.

Originally Posted by Ms_Jam

Third, I suppose I could have hit the emergency lights switch. Might have got a flash or two off before impact..

chances are this muppet wasn’t paying attention and it would have only made a big impact a smaller impact at best

Originally Posted by Ms_Jam

Fourth, would a loud horn have helped? One of the very few criticisms I have of the Fiesta is its polite little horn. Otherwise it is an outstanding vehicle IMHO...

I doubt it would make a difference, the horn is largely directional in the way it projects sound, as its in the front of the vehicle the should is projected forward (the car it's self acts as a giant sound shield in terms of rear ward projection)

Originally Posted by Ms_Jam

Fortunately I always leave more than a bit of space between my car and the one in front.?

This is the best thing you can do and by doing so you single handedly helped prevent less damage to your car and greatly reduced the chance of injury to your self

As long as no one was hurt and your car was in road worthy condition prior to the incident you can sleep well in the knowledge you did every thing you can to both prevent and accident and also reduce the risk of injury to others when this happens

[FgNewbie]

Originally Posted by kypez

How long is a piece of string?! You can never really know because it depends on the car you are in, the type of vehicle that hit you, tyre condition, road surface, and so in and so forth.

kypez that is reasonable. Keeping your answer in mind and with the information available... if you were in the OP's position, would you release the brakes as some suggest?

[FgNewbie]

Originally Posted by The Yeti

Lets say you did have time, and you footed it up on to the median strip, or out of that lane in to the flow of traffic, had you damaged your car and this other car had not hit you, you would be the one paying for the repairs to your car and any other damage you did, not the guy that now only nearly hit you.

If someone was definitely going to slam me, instead of worrying about who pays, I'd be more concerned with taking the action that would leave me with the least possible injury.

Originally Posted by The Yeti

I doubt it would make a difference, the horn is largely directional in the way it projects sound, as its in the front of the vehicle the should is projected forward (the car it's self acts as a giant sound shield in terms of rear ward projection)

The driver behind may not hear it but the driver up front may wake up and move off. Who knows what they were doing.

[kypez]

Originally Posted by FgNewbie

kypez that is reasonable. Keeping your answer in mind and with the information available... if you were in the OP's position, would you release the brakes as some suggest?

If I was in the OP's position, I'd go by my first post. I'd have made sure I had given myself enough room that if I saw some twit coming at me fast, I'd be able to move a couple of meter's forwards without actually impacting the vehicle in front of me. Trick is, eyes off the mirror then, and look forward and move as close as possible to the car in front. After that, it all depends on the car behind you but you have given yourself the best chance.

As was said, the OP had two cars ahead and hence there was little if any chance of ending up mid intersection and getting T Boned. Even if you are the first car at the lights, giving yourself 6 feet from the line will still see you activate the sensors for the lights to change and even then, you have room to move forwards without ending up in the middle of the intersection. I'd go forward and then brake (edit: but not full pressure, thus allowing movement but not entirely leaving the car to the will of the vehicle that hit me).

The only issue with releasing brakes (edit: completely) though is that you can have double whiplash from getting hit from behind and then hitting something in front. You have to make a conscious decision to keep your head on the headrest to avoid that.

I'm curious though, does the ABS then unlock the brakes when a car is being pushed and your foot is planted hard on the brake peddle? Or do you get pushed with locked brakes?!

[FgNewbie]

I'll opt out rather than go around in circles.

[kypez]

Originally Posted by sudszy

If the car is prevented from moving, more of that energy is used to deform the panels and another portion of it is used in changing the speed of the body the car is partially anchored to, in this case the earth.

Injuries dont result from the car getting crushed, they result from sudden changes of speed of the car, or blunt trauma injuries.

Perhaps think of what would happen if the car that was hit was parked in front of a brick wall and couldnt move, it would be sandwiched from both ends, provided the passenger cell stayed in tact, the occupants wouldnt suffer any speed change at all and would walk away unscathed, putting the brakes on isnt as effective as having a brick wall in front of the car, but it helps.

Sudszy, couple of issues with the physics you have applied. If the car was moving forward, or allowed to move, there is a difference in transferred energy between the two vehicles as you are not moving a resistant object, ie, the transferred energy is being realised in a different way. If it changed to acceleration, there is less energy to absorb into the structure of the body of the vehicle being hit.

The problem with your brick wall example is that you are taking that the entire human body is secured in a car which is not the case (head, arms and legs). The crumpling of the front of the car is "movement forwards" which then results in your body moving forwards. Depending on the momentum and kinetic energy of the object that hits you, you can be accelerated VERY quickly and end up experiencing the same retardation as hitting the wall moving. Just because you're sandwiched doesnt mean you do not accelerate (or move) and prevent injury.

So if the wall wasnt there or there was a "softer wall" (ie, another car infront of you) and you were allowing the car to move a little, you would thus experience less impact on yourself thus reducing your injury as opposed to sitting there with the brakes on.

Hope that makes sense...

[kypez]

Originally Posted by FgNewbie

I'll opt out rather than go around in circles.

Isnt that how most threads run!?

[sudszy]

Originally Posted by kypez

Sudszy, couple of issues with the physics you have applied. If the car was moving forward, or allowed to move, there is a difference in transferred energy between the two vehicles as you are not moving a resistant object, ie, the transferred energy is being realised in a different way. If it changed to acceleration, there is less energy to absorb into the structure of the body of the vehicle being hit.

Sorry did I say otherwise?

Originally Posted by sudszy

If the car is allowed to accelerate forwards the energy is still transferred to the car, it changes into kinetic energy..

Originally Posted by kypez

The problem with your brick wall example is that you are taking that the entire human body is secured in a car which is not the case (head, arms and legs). .

Yeh, I was, I didnt anticipate anyone sitting on the roof or bonnet, they are getting hit from behind, what part of them would be outside the car?

Originally Posted by kypez

Depending on the momentum and kinetic energy of the object that hits you, you can be accelerated VERY quickly and end up experiencing the same retardation as hitting the wall moving. Just because you're sandwiched doesnt mean you do not accelerate (or move) and prevent injury.

So if the wall wasnt there or there was a "softer wall" (ie, another car infront of you) and you were allowing the car to move a little, you would thus experience less impact on yourself thus reducing your injury as opposed to sitting there with the brakes on.

Hope that makes sense...

Not at all, the front of the car is being stopped from moving by the wall, hence the passenger compartment doesnt accelerate at any appreciable rate.

In the end the idea is to stop the passenger cell from accelerating, that is what causes the injuries, if it stays intact and doesnt accelerate at too great a rate, its very hard to get injured. Focus on what happens to the passenger cell rather than getting yourself confused with where the energy of the collision may or may not go.

The more we restrict the passenger cell from changing its motion or changing its motion at a slower rate, the better off the occupanst will be, which is also the function of the crumple zones of both the rear of the car and the front of the other car, to increase the time that it takes to change the motion of the cars. If you allow the vehicle being hit to be unbraked, it will accelerate forwards at a much higher rate, that's what causes injuries...whiplash, concussions, backs etc.

Its also the reason why you are not going to get injured if you are the driver of a truck that gets rammed from behind by a ford focus, there is just too much mass in the truck for it to accelerate appreciably and neither do the occupants.

Newtons law's and indeed the law of conservation of momentum are not negotiable here, the bigger the mass always enjoys a smaller speed change in a collision.

You can make a small mass behave like a heavy mass in collisons if it is connected to heavier masses, ie having the wheels "connected" to the earth or prevented from moving by objects in front of it.

[sudszy]

Originally Posted by aussie muscle

you should know hitting a solid immovable object is more painful than something softer, lighter or moving..

You are looking at the collision from the point of view of the person that does the rear ending, they affectively suffer a higher change in speed if the vehicle in front is braked, because they have effectively hit something that is more resistant to movement, just the same as if they had hit a larger vehicle and hence their collision is "harder" and so would be the injuries.

The people in the heavier vehicle, or the vehicle "connected" to the ground dont suffer as high a speed change and hence their collision is more survivable.

[geckoGT]

Originally Posted by LTDHO

Perfect advice, I do the same.

It's true, I'd rather the car be at a panel beater or wrecking yard than me in hospital or morgue!

I think many here need to understand that panel damage on a car is not directly proportional to the damage on the occupants.

In order to discuss this logically we first have to make some assumptions based on averages.

The first of these is that at point of imact in the vast majority of crashes, the impact speed is much less that the posted speed limit.
Second, by far the least amount of fatalities and serious injuries occur in rear end collisions.
Third, the vast majority of intersection crashes involved passenger vehicles of similar mass, not truck/bus v car.

Now that we have that understood, challenge those statements if you wish but you will find the evidence is there to support it. Now let's look at crash dynamics.

Firstly the majority of serious injuries or fatalities occur in the front seats plus these positions have the vastly greater occupancy rates. In the front seat on the average passenger car you have approximatey 60% of the vehicle behind the front seats, 40% to the front (remember your body extends all the way to the firewall). This means that in the rear impact you have about 10% more crumple zone to absorb impact before force is applied to the occupant. You also have the greatest portion of the passenger cell behind you which is structurally the strongest part of the modern car, they are designed that way. End result is the occupant is at an advantage in the rear end collision in terms of crash survivability and the stats support this.

At normal road speed, rear end collisions in appropriately spaced vehicles at a stop, having the foot brake applied at the intersection both reduces the likelihood of rear collision because of illuminated brake lights and decreases the risk of impacted car being pushed into the car ahead of it.

For the next bit you have to understand injury patterns are indirectly related to the extent of the vehicle damage, more vehicle damage does not mean more injury, often it means less injury. The only factor that directly causes injury to the occupant is the amount of force and the number of forces applied to the occupant. By releasing your brake prior to the crash and allowing your car to move without resistance you will save some panel damage at the rear of the car. Instead of that energy imparted on your car bending panels it will move the car. The problem with this is without that energy being absorbed, for example by the friction of the brakes and tyres you will simply travel at speed at the next obstacle without energy dissipation. The result will be that you hit the next obstacle (the car in front of you) with the remainder of the sum total of all the energy imparted on your car. The disadvantage from an injury point of view is now you have not reduced the sum total of all the energy of the crash, you have just changed it from a single vector in the rear collision to a double vector of a rear crash followed by a frontal crash. So really all you have done is borrowed some energy from the rear crash which is less likely to cause injury and passed it to a frontal crash which is more likely to cause injury.

One very important factor in crash injury patterns that no one has mentioned so far is the surface area that forces are applied to the body. In a frontal crash the force is applied to the body over the surface area of the seat belt only, maybe the air bag as well if you contact it. Also in the frontal crash the head and neck are unrestrained in the forward motion (no Hans devices in passenger cars), which applies significant force to the neck. In a rear collision the force is applied to the body over the entire surface area of the seat which is much larger than the seat belt (not to mention padded too) and proportionally less likely to cause injury. Also in the rear collision as the force is applied from rear to front the padded head rest contacts the head which not only absorbs impact but helps to support the head and neck, reducing forces on the neck and maintaining spinal alignment. If you were to see the impact coming and brace your back against the seat and your head against the head rest, there would he even less uncontrolled movement of the body and less chance of injury. The moment you allow uncontrolled forward movement of your car, the more changes in direction of the forces occur and the more injuries that become likely.

Now this is a car enthusiast forum an we love our cars so let's look at it from the point if view of our pride and joy. If an equal mass car hits our rear at for example 60 km/h and you have your brake applied, you will have extensive damage and the car will probably be a write off. If you are involved in the same crash but no brakes applied you will be pushed forward which will reduce the damage to the rear but unfortunately the remaining energy will be applied to the car in front if you. This will just result in damage to both ends of your car and it will still be a write off.

Basically in the act of releasing the brake before impact the only thing that you achieve is increasing your chances of injury as well as increasing the chances of injury to the person in front of you, but either way your car still dies. Sorry but I fail to see the logic in that.

[93EB_SXR6]

Just waiting for a moderator to close this thread.
I think the OP did all he really could.

[geckoGT]

Originally Posted by Professor_Evans

Just waiting for a moderator to close this thread.
I think the OP did all he really could.

Very true, there is not much you can safely do except brace.

I just had to comment on this stupid idea of releasing the brakes.

By the way, I asked my other half (who spent many years in insurance) if you can be liable for the car in front in a nose to tail. Her answer was that if you are stopped too close or do not have your brakes applied, or any other illegal act that contributes to that cars involvement you can be held responsible for that car.

[93EB_SXR6]

Yeah, I would have thought the insurance company wouldn't cover you if your brakes weren't engaged.

[93EB_SXR6]

I'd like to add that cars are just material objects.
People, however can't be replaced.
If it was a choice between wrecking my beloved HR or causing a long-term disability to someone (let alone fatality), I'd immediately choose for my car to be crushed.

Sorry for being so PC btw.

[LTDHO]

Originally Posted by Professor_Evans

Yeah, I would have thought the insurance company wouldn't cover you if your brakes weren't engaged.

They would not deny your claim.
If they did, I'd be interested to know why.

Originally Posted by Professor_Evans

I'd like to add that cars are just material objects.
People, however can't be replaced.
If it was a choice between wrecking my beloved HR or causing a long-term disability to someone (let alone fatality), I'd immediately choose for my car to be crushed.

Sorry for being so PC btw.

That's pretty much what I tried to say previously.

[kypez]

Originally Posted by geckoGT

I think many here need to understand that panel damage on a car is not directly proportional to the damage on the occupants.

In order to discuss this logically we first have to make some assumptions based on averages.

The first of these is that at point of imact in the vast majority of crashes, the impact speed is much less that the posted speed limit.
Second, by far the least amount of fatalities and serious injuries occur in rear end collisions.
Third, the vast majority of intersection crashes involved passenger vehicles of similar mass, not truck/bus v car.

Now that we have that understood, challenge those statements if you wish but you will find the evidence is there to support it. Now let's look at crash dynamics.

Firstly the majority of serious injuries or fatalities occur in the front seats plus these positions have the vastly greater occupancy rates. In the front seat on the average passenger car you have approximatey 60% of the vehicle behind the front seats, 40% to the front (remember your body extends all the way to the firewall). This means that in the rear impact you have about 10% more crumple zone to absorb impact before force is applied to the occupant. You also have the greatest portion of the passenger cell behind you which is structurally the strongest part of the modern car, they are designed that way. End result is the occupant is at an advantage in the rear end collision in terms of crash survivability and the stats support this.

At normal road speed, rear end collisions in appropriately spaced vehicles at a stop, having the foot brake applied at the intersection both reduces the likelihood of rear collision because of illuminated brake lights and decreases the risk of impacted car being pushed into the car ahead of it.

For the next bit you have to understand injury patterns are indirectly related to the extent of the vehicle damage, more vehicle damage does not mean more injury, often it means less injury. The only factor that directly causes injury to the occupant is the amount of force and the number of forces applied to the occupant. By releasing your brake prior to the crash and allowing your car to move without resistance you will save some panel damage at the rear of the car. Instead of that energy imparted on your car bending panels it will move the car. The problem with this is without that energy being absorbed, for example by the friction of the brakes and tyres you will simply travel at speed at the next obstacle without energy dissipation. The result will be that you hit the next obstacle (the car in front of you) with the remainder of the sum total of all the energy imparted on your car. The disadvantage from an injury point of view is now you have not reduced the sum total of all the energy of the crash, you have just changed it from a single vector in the rear collision to a double vector of a rear crash followed by a frontal crash. So really all you have done is borrowed some energy from the rear crash which is less likely to cause injury and passed it to a frontal crash which is more likely to cause injury.

One very important factor in crash injury patterns that no one has mentioned so far is the surface area that forces are applied to the body. In a frontal crash the force is applied to the body over the surface area of the seat belt only, maybe the air bag as well if you contact it. Also in the frontal crash the head and neck are unrestrained in the forward motion (no Hans devices in passenger cars), which applies significant force to the neck. In a rear collision the force is applied to the body over the entire surface area of the seat which is much larger than the seat belt (not to mention padded too) and proportionally less likely to cause injury. Also in the rear collision as the force is applied from rear to front the padded head rest contacts the head which not only absorbs impact but helps to support the head and neck, reducing forces on the neck and maintaining spinal alignment. If you were to see the impact coming and brace your back against the seat and your head against the head rest, there would he even less uncontrolled movement of the body and less chance of injury. The moment you allow uncontrolled forward movement of your car, the more changes in direction of the forces occur and the more injuries that become likely.

Now this is a car enthusiast forum an we love our cars so let's look at it from the point if view of our pride and joy. If an equal mass car hits our rear at for example 60 km/h and you have your brake applied, you will have extensive damage and the car will probably be a write off. If you are involved in the same crash but no brakes applied you will be pushed forward which will reduce the damage to the rear but unfortunately the remaining energy will be applied to the car in front if you. This will just result in damage to both ends of your car and it will still be a write off.

Basically in the act of releasing the brake before impact the only thing that you achieve is increasing your chances of injury as well as increasing the chances of injury to the person in front of you, but either way your car still dies. Sorry but I fail to see the logic in that.

I see your point. Agreed.

Just one extra question though. having this situation with room to move infront, why would you want to just be an immovable object? Wouldn't you allow for most transfer of energy be to the body and then allow for "forward give" to let some of it dissipate as forward motion thus reducing even more the forces on you?

Edit: by Give I mean still applying the brakes but at 80% braking rather than full push.

[geckoGT]

Originally Posted by kypez

I see your point. Agreed.

Just one extra question though. having this situation with room to move infront, why would you want to just be an immovable object? Wouldn't you allow for most transfer of energy be to the body and then allow for "forward give" to let some of it dissipate as forward motion thus reducing even more the forces on you?

Edit: by Give I mean still applying the brakes but at 80% braking rather than full push.

Good question. Do you think that in the stress of the moment you would accurately be able to modulate 80% brake pressure? I would suggest with the adrenaline of the moment the average person would not, it takes considerable practice and experience to think clearly in high stress situations, not something that comes naturally.

Personally I think you would be better off planting the brake with max pressure thus using both legs to push your body against the seat and reducing your body movement on impact. The most important thing is to push your head hard against the head rest and keep that pressure until the car has settled after impact, your highest risk in this type of crash really is your head and neck. Trying to think of modulating brake pressure may cause you to forget to do this.

In such a crash, tyre slip after impact would provide effective dissipation of energy through friction, releasing a bit of brake pressure is unlikely to enhance this to any appreciable amount. I guess another method that is legal is to apply the hand brake and brace both feet against the firewall. This would provide some resistance to forward movement but only half as only 2 wheels are braked so you are still going to hit the car in front with twice the energy you would compared to having the foot brake applied. Much more than that actually as the park brake is no where near as effective as the foot brake in any car (particularly B series falcons). Personally I would plant the foot brake and brace.

This all reminds me of a crash I attended where a small suzuki hatch was rear ended at speed by a B Double, the driver in the hatch was stationary and on the brakes at the time as shown by the skid marks at the point of impact. She was knocked clean across a 6 lane intersection and walked away without a scratch, the car was obviously a write off. Moral of the story is that rear collisions are very survivable.

[geckoGT]

Originally Posted by LTDHO

They would not deny your claim.
If they did, I'd be interested to know why.


That's pretty much what I tried to say previously.

They would still cover you but as you would be at least partially at fault (they can award joint responsibility) you would have an excess to pay and loss of no claim bonus.

[MAGPIE]

3 times cars I own have been rear ended, never has the person driving at the time been questioned as to whether they had the brakes applied at time of impact.

[The Yeti]

Originally Posted by FgNewbie

If someone was definitely going to slam me, instead of worrying about who pays, I'd be more concerned with taking the action that would leave me with the least possible injury.

The driver behind may not hear it but the driver up front may wake up and move off. Who knows what they were doing.

um Ok

I'm getting the impression based on your eariler posts that you just want to disagree with peoplr

go sick man I dont really care

[sudszy]

Originally Posted by MAGPIE

3 times cars I own have been rear ended, never has the person driving at the time been questioned as to whether they had the brakes applied at time of impact.

I suppose it would have only been an issue if the car was shunted forwards and collided with something else, was there any sequential collision? Im not really in the know if you would be liable for the damage caused or it would all be due to the person that did the rear ending.

Basically in normal driving the brake is only applied firmly enough to stop the car creeping against the auto, and as far as I know that is all that is required on any driving test

The person that runs into you certainly cant cry foul if they weren't applied, it would reduce the severity of their accident anyway.

[FgNewbie]

Originally Posted by The Yeti

um Ok

I'm getting the impression based on your eariler posts that you just want to disagree with peoplr

go sick man I dont really care

It could be boring if we all agreed or thought the same; possibly more peaceful.

I'm not sure which bit you didn't like. That I care less about vehicle damage and expense than injury or my willingness to use a (loud) horn which we both agree will be better heard by those blocking an escape.

kypez's reply to my question was more convoluted than I could respond to so I opted out. Conversely, I could have happily replied endlessly until I managed to convey my actual point.

Speaking of which, some of my own beliefs have been very eloquently expressed within geckoGT's own posts 76 & 83. Kudos to geckoGT.

Occassionally I'm reminded to avoid poor delivery, anything else is optional. Enjoy

[LTDHO]

Originally Posted by geckoGT

They would still cover you but as you would be at least partially at fault (they can award joint responsibility) you would have an excess to pay and loss of no claim bonus.

No they wouldn't, sorry.