>>>"The body and frame are designed with crush/crumple zones and roll-over protection, and the tandem seating means large side crush zones. Volkswagen claims protection comparable to a GT racing car. The car has anti-lock brakes, airbags with pressure sensors, and stability control." - in a car that weighed 290kg empty.
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>Trouble is that the laws of physics are more interested in mass and momentum than in crumple zones. When a two-ton behemoth rear-ends the 290kg vehicle, the lighter vehicle changes trajectory quickly enough to disengage neck vertebrae while the SUV driver brakes to a halt and says "ooh, what was that."

As a mechanical engineer I understand that argument, and it's true that a safely-designed massive vehicle fares better than an equivalently safely-designed light vehicle in the general case.

To be precise, crash safety primarily boils down to two things:

- providing a cell that resists deformation and penetration, thereby mechanically protecting the occupants
- keeping acceleration forces below critical levels

In your example the light vehicle would be accelerated from zero to (say) 50 km/h in the length of its rear crumple zone. It's not impossible to manage that; YouTube has examples of stock and Indy cars hitting the wall at 150+ km/h (accelerating from that speed to zero in the length of that vehicle's crumple zone) with the driver basically walking away.