[anb]

Originally Posted by RadixLecti

My understanding is:

See 'Method of testing', point 1. It states 'Deformable barrier'. This means that the barrier is not stationary once the collision has occurred.

If it's meant to simulate a car of the same weight, I presume that the barrier is adjusted in some way (thickness and/or strength) based on the weight of the car.

This is the case when two balls collide when one is in motion and the other one is stationary. See the Seltos crash test video. The barrier remains stationary even after the impact

[shancz]

Originally Posted by RadixLecti

'Deformable barrier'. This means that the barrier is not stationary once the collision has occurred.

This means that the barrier (the metallic looking structure that the car crashes into) deforms/crumples on impact.

Here is a GNCAP video, see the deformable structure in blue.
Credit to the providers of the video.

frontal offset crash test GNCAP

Here is a video which shows the non-deformable/rigid barrier, note that it doesn't deform/crush upon impact, only the car does.
Credit to the providers of the video.

small overlap crash test IIHS

[JediKnight]

Originally Posted by anb

I am not able to understand this . The force due to the accident is because of change in momentum. Here the car is impacted against a stationary object . Since the velocity of the object is zero, the weight of the object doesn't have an effect on accident since momentum of the stationary object is zero.

When two objects of unequal mass collide the object with lesser mass object gets a higher impact impulse. Example if a loaded truck hits a small hatch, the truck driver would just experience a slight thud, but the impact on the small hatch will be so severe that it would probably be crushed beyond recognition. So a heavy vehicle with the same or lesser safety score may be safer when colliding with lighter vehicle with same or more safety score.

In the test probably you are colliding with a stationary object or a a simulated object of equal mass. But in real life most likely the collision will be between unequal masses. Hence in real world a heavier vehicle is likely to be safer with the same safety or lesser safety rating when compared to a lighter vehicle with same or even more safety rating.

[sureshkishore]

Thanks for the excellent information, it certainly helps to clear lot of doubts regarding GNCAP.
I hope mass manufacturers bring in Collision avoidance system such as radar guided automatic braking soon to entry level cars too.

Does Maruti have any car with 4 channel ABS?

[superguy282]

Originally Posted by anb

This is the case when two balls collide when one is in motion and the other one is stationary. See the Seltos crash test video. The barrier remains stationary even after the impact

I do not about the exact Physics behind this (I request BHPians who may know to kindly share). However multiple real world experiments have shown that the forces acting on the car when collided with a deformable barrier are similar. The barriers were then fine tuned to be even more accurate to the said scenario. Which is why, the ratings shouldn't be compared. To quote the IIHS(on whom NCAP is after all, based)

In the moderate overlap frontal test, a vehicle travels at 40 mph toward a barrier with a deformable face made of aluminum honeycomb. The barrier face is just over 2 feet tall. A Hybrid III dummy representing an average-size man is positioned in the driver seat. Forty percent of the total width of the vehicle strikes the barrier on the driver side.

The forces in the test are similar to those that would result from a frontal offset crash between two vehicles of the same weight, each going just under 40 mph.

Frontal crash test results can't be used to compare vehicle performance across weight classes. That's because the kinetic energy involved in the moderate overlap and small overlap frontal tests depends on the speed and weight of the test vehicle. Thus, the crash is more severe for heavier vehicles.

Given equivalent frontal ratings, the heavier of two vehicles usually offers better protection in real-world crashes. In 2009, IIHS demonstrated this principle with a series of tests in which small cars were crashed into larger cars, all of which had good frontal ratings in the moderate overlap test.

Source: Link

Originally Posted by sureshkishore

Thanks for the excellent information, it certainly helps to clear lot of doubts regarding GNCAP.
I hope mass manufacturers bring in Collision avoidance system such as radar guided automatic braking soon to entry level cars too.
Does Maruti have any car with 4 channel ABS?

As pointed out by other members, all cars currently sold (or sold after the safety reforms)in India have 4 channel ABS.

[GeeTee TSI]

Originally Posted by Rahul Bhalgat

don't be more confident because of better GNCAP while traveling wih a child. This is because most of us (almost all of us) don't use any dedicated child seats.

Very pertinent observation.

Just like an attitudinal change is probably being brought about by GNCAP that there is something called crash worthiness, the whole exercise is futile if the occupants are unrestrained. I fervently hope child seats are offered by dealerships as an accessory for families with children (will be quite evident to them during the purchasing process).

There are safety ratings for child seats too to be considered as they should not be the weakest link. Does NCAP publish those?

[giri1.8]

We should also have in mind that, crash test ratings should only be a part of the thought process while choosing a car, if someone wants a good highway cruiser that can do 100+km/hr all day, then choosing Thar over something like the Creta top end won't be necessarily a safer bet.

[superguy282]

Originally Posted by GeeTee TSI

Very pertinent observation.
Just like an attitudinal change is probably being brought about by GNCAP that there is something called crash worthiness, the whole exercise is futile if the occupants are unrestrained. I fervently hope child seats are offered by dealerships as an accessory for families with children (will be quite evident to them during the purchasing process).
There are safety ratings for child seats too to be considered as they should not be the weakest link. Does NCAP publish those?

AFAIK, NCAP themselves haven't published anything(I may be wrong) that indicate different child seats have different ratings. However there are many guides as to what type of seat to use (according to the age of the child) and how to use them properly to get the desired safety.

Here is a guide by the NHTSA indicating the usage by age.

Originally Posted by giri1.8

We should also have in mind that, crash test ratings should only be a part of the thought process while choosing a car, if someone wants a good highway cruiser that can do 100+km/hr all day, then choosing Thar over something like the Creta top end won't be necessarily a safer bet.

I am two minds about this. The Thar isn't a vehicle too be used above 100 km/h, but that is more due to the driver not being able to effectively control the vehicle above those speeds. Thus increasing the chances of a crash. How it may fare incase of crash will differ. Regardless, I seem to agree with you.

[lina]

Originally Posted by anb

I am not able to understand this . The force due to the accident is because of change in momentum. Here the car is impacted against a stationary object . Since the velocity of the object is zero, the weight of the object doesn't have an effect on accident since momentum of the stationary object is zero.

Yes, but in real life it will. For a heavier car, a lighter car wont act like a stationary object. It can plow through because of its momentum, thus making it safer by default.

[pseudo_coder]

What an informative thread! Journalists should learn to write like this, instead of feeding us with click baits.

I didn't understand the logic of 'deaths per square foot' of car. Many cars are occupied by a single person, regardless of the car size. So a fatal accident in the bigger car will register less deaths per square foot. Am I missing something?

[ssenhyd]

Originally Posted by superguy282

Misconceptions about GNCAP

I
Conclusion
A 5 star safety rating doesn't guarantee safety in all scenarios and situations.

Hi superguy.
I can't thank you enough for taking the time and posting these very informative article postings.
I learnt a lot from your postings.
Thanks for the public service!

[superguy282]

Originally Posted by pseudo_coder

I didn't understand the logic of 'deaths per square foot' of car. Many cars are occupied by a single person, regardless of the car size. So a fatal accident in the bigger car will register less deaths per square foot. Am I missing something?

It was meant to indicate that more people have died in smaller cars (having less area) than those in bigger cars. So yes, a fatal accident in a bigger car will have lesser deaths because it is big. The occupancy of the car has nothing to do with it.

The whole method was pretty unusual and different from conventional charts, which is why I thought about including it.

[gauravanekar]

Let me pitch in try clear some misconception in this thread.
A car hitting a solid wall without a deformable barrier is equivalent to two cars of same mass colliding each other but the twist is that the car you are hitting is perfectly rigid car which doesn’t deform at all. This is not true representation of real life crash.

So the tester has to simulate the crumple zone of the incoming car, that is why a deformable barrier is placed in front of solid wall. The combination of solid wall with a deformable barrier approximately simulates a car of equal weight getting involved in crash.

As far as assessing the crash safety of two cars of unequal weight is concerned, heavier car is always safer compared to lighter car.

If the tester wants to simulate crash of unequal mass cars, the main barrier (wall) should not be fixed and it should apply momentum on the backside of deformable barrier on its own. Negative momentum ( away from deformable barrier) if the incoming car is lighter, positive momentum if heavier

[RadixLecti]

This is the case when two balls collide when one is in motion and the other one is stationary. See the Seltos crash test video. The barrier remains stationary even after the impact

Apologies, I obviously worded my response poorly and in a hurry. When I said "does not remain stationary" I did not mean that the barrier moves bodily along the floor - as in the two balls example. But deformation requires that energy be transferred. In this case it comes from the kinetic energy of the car.

The 'crash face' of the deformable part begins moving towards the 'rigidly attached' face at impact. Mass in motion requires that kinetic energy be present and this energy is used to do the work of deforming the barrier.

So some of the momentum at impact is transferred to the deformable barrier, meaning that the front crumple zone of the car has to absorb less energy than in the case of collision with a non-deformable barrier (AKA a wall).

This means that the barrier (the metallic looking structure that the car crashes into) deforms/crumples on impact.

Here is a video which shows the non-deformable/rigid barrier, note that it doesn't deform/crush upon impact, only the car does.

Thanks, I do understand the difference. I responded hurriedly, as explained above.

[ravradha]

A well-articulated post on how to evaluate for ourselves, and, what safety rating means absolutely and relatively with respect to the size of the car.

In the comprehensive scheme of safety and risk factors before the crash, during the crash and after the crash, William Haddon has come out with what is called as Haddon Matrix published in the WHO - Road safety training manual.

In multiple posts, we have mentioned the importance of human factors as the primary safety guard. Haddon matrix puts into perspective, in the overall safety the car safety is but a small essential part. Strangely driving skill is missing from that. He seems to have clubbed it with attitude.