Typically, when the IIHS or Euro NCAP tests two cars safety capabilities against each other’s, it’s a test of two cars crashing into the same object, independently, and seeing which car fared better. However, in this case, we’re taking a look at how two cars performed after accidentally crashing into each other. Fun.
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InsideEVs has an interesting story about a BMW i3 owner who was rear-ended by a driver in a Cadillac CTS moving at a very serious rate of speed. Now, considering that the second-gen CTS weights almost 1,000 pounds more than a BMW i3 and that the CTS was moving fast enough to hurl the i3 173 feet upon impact, you’d expect the Cadillac to have one the battle. If that’s what you expect, you’d actually be wrong.
See, the BMW i3 uses a CFRP (Carbon Fiber Reinforced Plastic) passenger cell that is made from one single piece. Attached to this passenger cell are the aluminum subframes that hold the wheel carriers and what not. So there aren’t many parts of the i3 that are welded, riveted or bonded together, making its structure very stiff. CFRP is also stronger than steel.
The i3 also has a large advantage over any gasoline or diesel powered car, as there aren’t any engines or transmission or exhaust pipes. There also aren’t any oil pans, radiators, coolant tanks or fuel tanks. Being that there’s a considerable lack of mechanics in an electric vehicle like the i3, automakers have a lot of space to build in a lot more safety equipment, like crumple zones and impact absorbers. This allows EVs to be much safer and one of the reasons why the Tesla Model S crushed the IIHS safety tests when they first tested it.
So when the CTS slammed into the back of the i3, yes the i3 was sent flying forward 173 feet but was barely damaged in comparison to the CTS. The rear bumper was smashed up, but the hatch was still able to power open via the remote. All the doors still opened perfectly, because there can’t be any body flex due to the single piece carbon fiber passenger tub. Some interior bits, like the seat backs and and center arm rest were broken due to impact, but the structure of the car was completely intact, thus saving the passenger’s life. The driver of the i3 walked away with nothing more than a stiff neck, while the CTS driver was taken away in an ambulance. The CTS was also clearly totaled, as the front end looked like origami.
This just goes to show how strong and rigid carbon fiber passenger cells are and that, despite its small size and light weight, the i3 is far stronger than it looks. So if anyone out there is considering a BMW i3 but is on the fence due to safety concerns for their family, as the car is so small, fear not. The BMW i3 was hit so hard that it was hurled 173 feet, or more than half of an American Football field, and the passenger had only a sore neck the following day. That’s impressive in any car, nevermind a sub-3,000 lb electric hatchback. You think SUVs are safe? Wait ’til they take on the i3.
[Source: InsideEVs]
The InsideEVs.com source article makes it clear that both the Caddy and the Bimmer drivers were taken away by ambulance. Also, since a car’s primary “crumple zone” is the front, the damage to both cars is as should be expected. As for the passengers of each vehicle, by the basic laws of dynamics, the Bimmer driver suffered greater acceleration forces than the Caddy driver because of the mass difference between the two vehicles. Fact remains, anyone who drives a light-weight vehicle is more prone to death and injury, all else being equal.
Agreed. Can’t beat physics no matter how hard you try. It’s not just a good idea, IT’S THE LAW!
So, so wrong. Your reasoning and the physics don’t match. The CTS hit the i3, coming to an immediate stop and transferring its kinetic energy all at once. The i3 released the kinetic energy it received from the CTS over time and distance (173 ft). If the i3 had been parked facing an immovable object (ie- brick wall) preventing it from releasing the energy over time, it would have been just as damaged as the CTS.
For example: if a person fell 30′ and hit concrete, they would experience injuries. If they fell the same distance onto a movie stunt airbag, they would be less or not injured. Why? The person is slowed by the airbag as their kinetic energy is dissipated over a couple seconds instead of all at once.
I’m not disagreeing with the point you are trying to make on deceleration and time – but you’re not applying that theory to a vehicle collision – These are two different deformable objects, you’re treating them as though they are two identical completely rigid identical masses (pool balls for example).
Firstly, the CTS would not have come to an immediate stop, rather trading momentum with the i3, accelerating the BMW as it itself was decelerated, so the duration of the collision was not 0. For an immediate stop you’d have to assume the i3 was an immovable object, which clearly, it wasn’t
The destruction to both vehicles shows that an amount of the CTS’s kinetic energy was dissipated during the collision, so had the i3 immediately hit a brick wall the kinetic energy available for that collision would still be less than the original collision – whether that would have left the i3 just as damaged as the CTS is almost irrelevant – it would be a more interesting proposition to ask what would have happened if the i3 had been parked facing the back of another i3!
How dumb is this article! Cars are meant to collapse in the front especially in the front quarter. The I3 was hit from the rear where a car is designed not to crumple. Also it is lighter so yes it can be hurled out of the way. Now if that had been over an embankment then the article would have read “I3 Driver Killed by…!”. No actually I take that back…..you would not have written it at all then.
What if’s?
What if the CTS driver had hit a school bus stop?
From the damage I see, both cars performed exactly how they should have in a collision. Yes the Cadillac is probably totaled. But in a collision, the concern is about how the car deforms in a controlled way so that the occupants are kept safe. The value of the car, or keeping it from being a total loss, is not a priority in these situations. With the i3, there is no room for the structure to collapse. So the force is taken through the small bumper and the seatback. Perhaps this is why the headrests in the i3 are so prominent.