Photo: ADACYou might have seen photos of crash tests in which two vehicles — two actual brand new vehicles — are crashed against each other by some safety rating agency. What should be kept in mind is that’s not how cars or SUVs get their safety ratings.
Such crash tests, with two production vehicles pitted against each other, might help develop actual test procedures. Plus, as they look like real-life crashes, they catch the viewer’s attention, and are a good way to illustrate a point. They are educational.
But the actual evaluation of a vehicle — determining its safety rating — is done by crashing it against a barrier.
And is the barrier stationary? Speaking about frontal crash tests only: in American tests, yes; in Euro NCAP tests, since 2020, not anymore.
It’s a trolley — with four wheels similar in size to those of a car or a SUV, a wheelbase slightly longer than in a typical European car, and weighing 1400 kg (about 3100 pounds) — still more than many compact hatchbacks on European roads. There is a deformable aluminum structure — the actual barrier — attached to the trolley’s front end.
Such trolleys, or “mobile barriers”, have been used in side impact testing for quite a long time (the barrier crashes into the side of a stationary car). But using them for frontal impact testing, as a standard procedure — that’s new. In the U.S., the NHTSA has been experimenting with mobile barriers for frontal impact testing for years; but, so far, hasn’t made them part of the test procedure.
The trolley is accelerated to 50 km/h (31 mph), while the tested vehicle is accelerated to the exact same speed in the opposite direction. The left part of the trolley’s front end collides (head on) with the left half of the tested vehicle’s front end.
The weight problem
It’s quite different from the old pre-2020 procedure, which wasn’t much different from the one still used by the American IIHS. To be exact, what I’m describing here is the “moderate overlap” or “moderate offset” frontal impact; both the IIHS and Euro NCAP use more than one scenario of frontal impact testing.
In the old procedure, instead of two moving objects — the tested vehicle and the trolley, both moving at 50 km/h (31 mph) — the tested vehicle was accelerated to 64 km/h (40 mph) and smashed against a stationary barrier.
And that old stationary barrier covered just 40% of the vehicle’s width — not 50%, like the new mobile barrier.
Cars, and SUVs, obviously don’t like crashing into narrow objects (such objects cut deep into the car’s structure) — so does it mean the new, wider barrier is actually less demanding? Not really, because the new barrier, while wider, is also lower — so the impact is still spread over a relatively small area (over a relatively small part of the car’s front end).
Also, the new barrier is made of harder material than the old barrier — more about that later.
But first, one obvious issue: the new barrier puts really small cars — like popular city cars — at a disadvantage.
In 2012, the German association ADAC tested four different tiny cars against the new barrier. Yes, in 2012, even though Euro NCAP adopted it only in 2020; development of crash test procedures in a slow process — maybe it does not need to be, but apparently those developing them preferred to give automakers some time to adapt.
These city cars — back then — boasted good Euro NCAP safety ratings; 4 or even 5 stars out of 5. Today, no car will get a good Euro NCAP rating if it’s not equipped with automatic crash prevention systems like automatic emergency braking or lane assist, no matter how well it does in the actual crash test (makes sense: it’s certainly better to avoid a crash than to be in a crash, no matter how safe the car). Back then, than policy was not yet in place — and the crash test results of these tiny cars did not look bad.
But when these cars were tested by ADAC against the new barrier, the results — to put it mildly — changed for the worse:
The best results are in green; then goes yellow, orange, brown/maroon, and red (the worst results). Image: ADACWhat happened?
Well, in the old EuroNCAP tests, these cars only had to carry their own weight, so to speak. And they were light. When smashed against a stationary barrier, the structure of such a car would only need to deal with stresses caused by a relatively light object — the car itself.
And then that small car would basically come to a stop; no bouncing off the heavier vehicle, no being dragged/pushed by the heavier vehicle.
No wonder small (and cheap) cars used to get better results than bigger ones.
But that changed with the new trolley-barrier setup, which simulates a collision with another vehicle quite realistically. Note that the trolley (fixed weight of 1400 kg/3100 lbs, no matter what vehicle it’s crashed into) is heavier than any of the four cars tested. It’s kind of obvious that in a head-on collision between two vehicles of different weights, the lighter vehicle is in a worse position. Because even if its body structure holds, the passengers inside the lighter vehicle are still subjected to higher forces during the crash.
It’s interesting, though, that the best result of the four — the least terrible result — was achieved by the Smart (a.k.a. SmartCar). Even though it’s the lightest one. Designers of the Smart knew that its low mass was going to be a problem in an impact. But they designed the vehicle with a stiff “safety shell” named Tridion — which solves at least one problem, that of structural integrity. As for the crumple zone, the car basically uses the crumple zone of the vehicle that it crashes into.
Different dimensions and greater hardness of the new barrier might have contributed to these results, though. The new barrier is harder, and it also strikes slightly lower:
Left: old barrier. Right: new mobile barrier. Not exactly to scale. Data for the new barrier based on the prototype used by ADAC. Material strength (in megapascals, MPa) for both barriers might be slightly inaccurate, by up to 10%. Image: IIHS, Euro NCAPThe new barrier (unlike the old one) is also a good measuring device: it measures how much damage the tested vehicle would do the other vehicle in the crash. Not with sensors or anything like that; the shape of the barrier after the crash, alone, allows for calculating the forces acting on each point of the barrier quite precisely. Since 2020, Euro NCAP notes in the description of the test results whether the vehicle is an aggressive, moderately aggessive, moderately benign or benign “crash partner” to another vehicle.
Heavy means safe?
All of this looks like bad news for tiny cars. And not only for those not built with the new barrier in mind; even completely new designs are going to suffer if they are much lighter than the new test trolley.
In 2021, so after the new barrier came into use, the Skoda Fabia (which was a budget city car, at least in its previous incarnation) got an excellent Euro NCAP rating. The video shows the car hitting the trolley and barely bouncing off it. Good engineering, sure, but that’s not the whole explanation. It looks as if the weight difference between the car and the trolley weren’t that big. And, as it turns out, the Fabia is relatively heavy — at 1200 kg (2650 lbs), it enters what used to be the European compact car territory…
But I’m not criticizing Euro NCAP for choosing what is essentially a more realistic test procedure. By the way, in addition to changes to the frontal impact test, the organization also changed the side impact test procedure in 2020. Now the car is impacted from the side at the speed of 60 km/h (37 mph), not 50 km/h (31 mph) like before. In the U.S., the IIHS experimented with side crash testing at both these speeds; so far, they haven’t changed the standard procedure, sticking to 50 km/h, or 31 mph; although they use a different, much taller barrier that better simulates the front end of a pickup truck.
Note: I don’t think introducing a mobile barrier for frontal crash testing in the U.S. would be a good idea — not right now. It would probably be much heavier than the European one, which would result in poor safety ratings of cars (as opposed to heavier vehicles like SUVs and pickup trucks). And I don’t want cars to become an extinct species in the U.S.
And the complete list of additions and changes that Euro NCAP made to their array of crash tests during the last 10 years is much longer than that. There is an increased focus on the safety of passengers in the rear seats — something that was mostly overlooked a decade ago.
To me, it looks like the ongoing shift toward EVs is going to help city cars in these tests. Because all that battery mass weighing electric vehicles down (that includes EVs that are city cars) now becomes an advantage.
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Sources: [1] (in German), [2],[3],[4]