IIHS is the acronym for the Insurance Institute for Highway Safety. This is an American organization founded in 1959 by insurance companies interested in understanding all aspects of highway safety. With their business built on insuring cars and drivers it makes sense that they have a greater understanding of accidents, damage and injury.
This link gives a good background on the IIHS and how it has evolved
One of the most publicly visible areas of IIHS work is their crash safety rating system, which is developed based on crash tests in their own testing facility. This rating has real world implications, with a 5 Star IIHS rating used by manufacturers as a selling feature and by insurers as a guide to setting insurance rates.
Manufacturers pay a lot of attention and will make design changes to address the issues that prevented them from getting top scores. You will be safer in a 2016 vehicle than you would be in a 2010 or 2005 vehicle in the same type of hit. You will probably be safer still in the 2017 because none of the manufacturers move backwards on safety.
The car may be somewhat more expensive to repair, but you will not care much about that if you walk away from the accident with no injury. Your insurance company should be ready to pay an extra $2,000 or $3,000 or even $10,000 to repair your car if tens or even hundreds of thousands in injury costs are saved.
5 Stars to 3
The insurance company should be ready to pay; but then we run into the real world of measurement and reward in a compartmentalized business. The insurance adjuster, and the entire claims department, is judged by the amount of money paid out; lower claim costs are viewed as a good thing and the in-depth quality of repairs is not yet measured.
John Huetter of Repairer Driven News goes into this discussion in more depth http://www.repairerdrivennews.com/2016/11/11/iihs-top-safety-pick-criteria-and-what-it-really-means-for-collision-repair/ and importantly attributes the blame for the current inadequate repair model equally to both repairers and insurers.
In the unregulated world that we work in the insurance companies are probably the best positioned to insist on a proper repair but the huge emphasis on cost is preventing them from doing this.
The first company to honestly address the issue of rating and insuring 5 Star cars and then accepting and paying for repairs that leave the car at a 3 Star level has yet to step forward. It is a big problem, but there are lots of very smart people on staff at insurance companies. They will figure it out but it will take time. There’s that 5 year timeline again