Some misinformation in here...
Insurance Institute for Highway Safety did the crash, not National Highway Traffic Safety. (insurance industry paid, not the government) Plus it was a Bel Air, not an Impala.
I have actually seen the 59 Bel Air in question, its still in the lobby at IIHS. NOT RUSTY. Also, to stem off the other one I hear a lot, the engine was NOT removed. Yup, it did that poorly. (somewhere I might have pictures I took of it)
https://www.youtube.com/embed/joMK1WZjP7g
Think about it, in the last 20 years we have seen a radical jump in materials, as well as computer aided design. Cars have been getting heavier, but only a bit larger. That weight has been going somewhere and that is heavier structure with better design. Crumple zones are finely engineered these days and I dont even need to start on the state of airbag technology.
These days we have multi-stage airbags, knee protection airbags, side impact bags, rollover bags. We also have seat-belt pretensioners, yup, theres a small explosive device in your seatbelt that cinches it down during a crash. (crashed a newer vehicle and the seatbelt wont retract after? thats why!). You also have redesigned head restraints that reduce neck injuries, with some being active where they deploy forward in a crash to protect your neck.
On top of that, new vehicles have Event Data Recorders (AKA Crash Data Recorders) contained within the occupant restraint controller. Crashes can be looked at and give data pre and post crash to determine the vehicle state and the forces enacted upon the car, so real world crashes can be analyzed to determine just why someone was injured. (dont fret, you have to sign a release or a police agency has to flex a warrant or something to have that read)
To answer another question...
https://www.youtube.com/embed/TEbmPsukEHI
https://www.youtube.com/embed/PVTI4tXHGYE
Fastest one there was 38mph...