Very little information exists.
No standard testing is done for crashes like this, except for a required test that is mostly designed to verify fuel system integrity.
There has been some concern over 3rd row seats that are close to the rear hatch, primarily for heavy adults in seating positions that do not have head restraints. The identified risk is that heavy adults can load the seat back to failure, and then are at risk of injury from intrusion. Ejection is another major concern.
Some articles on this topic were written in an attempt to panic consumers, so a few things should be noted:
1) Severe rear end crashes are rather uncommon, and tend to be only about 5% or so of all crashes.
2) If you are an adult in the third row, choose a rear seating position with a head restraint and a seatbelt system with a lap AND shoulder belt.
3) If you will regularly carry adult passengers in the third row, it does not hurt to select one that has at least a foot or two between the third row and the rear hatch.
In general, kids do not have the same level of risk in a third row as heavy adults:
1) Kids are much lighter, and much less likely to load the seatback to failure.
2) Kids in harnessed carseats or high back boosters will get some protection from intrusion from the shell of their child safety seat.
3) Kids in 5-point harness seats will have a much lower risk of ejection, which would be a main factor in striking the rear hatch.
As an adult, I would be very concerned about regularly seating myself in the third row of a vehicle if there was no head restraint or shoulder belt. This is especially true in one with only a few inches of space between the third row seat and the rear hatch. On the other hand, I would have little concern about placing my own child in a harnessed carseat in the third row.
Of much greater concern to me are side impacts. These tend to be much more common and severe than rear impacts. If you are in an outboard seating position, you are also very close to the point of impact and there is very little vehicle structure protecting you. Unlike a 3rd row in a rear-end crash, there isn't even the back of a seat between you and an impact. Choosing a vehicle with good side impact ratings and selecting child seats with reasonable side impact protection are important. A new set of side impact tests will be released by the IIHS this year.
If you are buying an SUV, rollovers are also a much greater risk to the passengers than rear impacts. Selecting an SUV with features like side curtain airbags across all three rows is a great safety improvement, and I would consider it necessary. Choosing one with head restraints and lap/shoulder belts for all occupants is a must. A good rollover rating and/or stability control is also a major improvement in your overall safety in any SUV.
So, my advice is to concentrate on side impact and rollover safety as those are a much larger threat to most occupants in the rear seats. If you find models that are equally safe in these areas, then by all means select one with third row head restraints, shoulder belts and an increased distance from the seat to the hatch
This should improve the safety for adult passengers in the third row.
I hope that helps! Also, see our family vehicle guide:
http://www.car-safety.org/family.html
