> The cyclist was launched headfirst into the bumper of a car stopped at the light and her helmet loudly cracked in two
Bicycle helmets "work" by deformation of the hard polystyrene foam. If it cracked in two, it failed. If the foam did not deform, no energy was absorbed.
It is an extremely common misconception, especially among cyclists, that a cracked/disintegrated helmet "worked" and "saved their life."
Bicycle helmets crack and fall apart in many of these crashes because they're not designed to take anywhere near the typical forces involved in actual crash. They're only designed to "work" for a stationary fall from about the height of an average adult male, falling straight upside-down on top of their head.
> I'm sure she would have died without that helmet.
That's not how that works.
"I saw someone wearing a bunch of ring of flowers around their head and they got hit by a car. The flowers exploded in a poof of pedals. I'm sure she would have died without the ring of flowers around her head."
"I wear a ring of garlic around my neck. I haven't been attacked by vampires. Garlic repels vampires!"
Etc.