Hmm, aren't there low hanging bars at bumper level on the side and end of the trailer, so that crumpling zones come into effect instead of decapitating the car with no chance of energy absorbtion through deformation (which seemed to not have been happening there)
I recall in Europe these became mandatory decades ago when a similar crash happened, killing one person, the family of which fought a long battle to have these bars become mandatory (which a couple of years later saved my father's life when he launched to overtake a truck, that suddenly decided to brake hard and turn left without notice at the last second).
Yes, underride or "Mansfield bars" (after actress Jane Mansfield who was killed in a similar accident).
Those are only rated for impacts to 35 mph. From the position of the Tesla in the image, it may have been travelling substantially faster.
The Tesla is also a deceptively massive automobile for its size, with much of that mass being low, in particular below the position of an underride bar, which might otherwise engage with the engine of a conventional vehicle. Effectively, the Tesla has a longer lever arm to apply force to the undderride bar. Whether or not that is a factor in Tesla-trailer collisons isn't clear, but might be something that warrants investigation and testing.
I recall in Europe these became mandatory decades ago when a similar crash happened, killing one person, the family of which fought a long battle to have these bars become mandatory (which a couple of years later saved my father's life when he launched to overtake a truck, that suddenly decided to brake hard and turn left without notice at the last second).
edit: seems like in 2015, 2% were killed this way in Germany (where it's been mandatory for decades) vs 16% in the US https://www.dekra-roadsafety.com/fr/protection-anti-encastre...