New cars are tested for crash worthiness as we know. They are usually rated from zero to five stars and people are greatly influenced by the results. Potential buyers may shy away from anything less than a five star rating.
My personal view is that too much is read into the system. Of course, a newly released car getting two or three stars today would be unacceptable but the difference between a four and five star rating may not be as people think. The reason is that it is very difficult to replicate all the nuances of 'real world' accidents when testing cars in controlled environment.
Now a new overlap test that puts only 25% of the front of a car into an object (at 40 kph) as opposed to say 40% has been carried out. It was done by the The Insurance Institute for Highway Safety, and the results were sobering. It seems that many manufacturers that trumpet safety, are simply very good at making their cars pass existing tests. This new test showed how few cars are made to stand up to a smaller object impact, such as would happen with a tree of power pole.
Poor: Mercedes C Class, Lexus IS and ES350 and Audi A4.
Marginal: Acura TSX, BMW 3 Series, Lincoln MKZ and VW CC.
Good: Acura TL and Volvo S60.
The above models are premium, the next batch of tests will be every day models, and it won't be pretty I suggest. Yet even some reputable models as listed above had unacceptably poor results. The IS and C-Class had sufficient structural deformation to trap the dummies feet while the door of the VW CC came off!
It seems that five stars can be achieved if you study standard tests and engineer cars to meet those. A common accident like hitting a power pole is for some reason not in existing tests. So car makers generally don't worry about making them safe for that scenario. That is cynical to me. One of the brands tested builds cars not just to get five stars but to make safe cars, and that is Volvo.
So if someone says they won't buy a four star car, well maybe it failed a technicality on the existing test, whereas a five star car might in fact be worse in certain accidents. If you are very concerned about safety, buy a Volvo.