Vehicle mass: What effet does it have in an accident?

[geckoGT]

Originally Posted by Brazen

Instead of ANCAP smashing cars to an imoveable wall- which is the equivalent of a Fiesta hitting an oncoming Fiesta and a Patrol hitting an oncoming Patrol.

They should smash the car into a moveable object which simulates the average car, ie the Fiesta is now hitting an object the weight of a Commodore and the Patrol is now hitting an object the weight of a Commodore.

I think it would be scary to see the difference in ratings...There is probably a bit of social pressure to not do this, as it would just encourage people to buy heavier and heavier cars.

You may have a very good point there as it would change things to a degree, the problem is as your mass and speed increses, your chance of survival decreases.

By that I mean all cars are built to withstand a certain force of impact and maintain good survivability. So a 5 star car maintains good survivability at a equivalent force of impact at 64 km/h. Once you go over that speed or increase the force from that level, chances of survival rapidly deteriorate as the structural integrity and crash protection of the vehicle is exceeded. Similarly if you were to keep the speed the same but increase the mass, perhaps 200 kg of cargo, your chance of survival decreases.

In this situation the vehicles own mass works against it in terms of vehicle safety. Think of the passenger compartment as the critical zone, the more mass in front and the less behind the critical zone, the less force that will push through the critical zone. The more mass behind the critical zone, the more force that will push through it once vehicle structure integrity has failed. Think of it this way, large rear wheel drive vehicles have a greater percentage of mass behind the passenger cell, small FWD have a higher percentage of mass in front of the passenger cell.

In a stark and over exagerated demonstration of this to illustrate a point, review these two clips.

The first is a smart car into a solid concrete barrier at high speed of 70 mph (112 km/h).
Smart Car Crash

Notice how on impact the car changes direction and actually bounces back off the wall without the back of the car pushing through the passenger cell, even to the point that the doors can still be opened. I would not want to be the occupant in this vehicle but considering the maintained integrity of the passenger cell, survival is possible.

In this next video it is a heavily loaded dual cab truck That was actually used as a wall test for future crash testing. In this video the test was apparently conducted at 65 mph (104 km/h).
Truck Crash

In this crash you will note how the cab completely fails, the fatality is almost certain as the heavily loaded back continues to move forward. With such momentum that it plants the truck against the wall and keeps pushing until there has been enough crumple zone to slow it, which occurred way past the passenger cell.

Now I will concede that the are many inequalities in the examples I have given, most notably it is a 1980's vehicle with 1 star rating if you are generous against a 2000's vehicle with a 5 star rating. Also the wall is of different construction but the smart car wall did maintain enough integrity to bounce the car.

Having stated those inequalities, I still think these videos do demonstrate the concept that mass behind the passenger cell can work against the aim of crash survival when the speed is enough to overcome the designed safety features of that vehicle, when crashed into a solid immovable object. Albeit to a spectacular level and not a level commonly seen on the street.