Not all bike accidents involve cars. Sometimes people hit rough pavement and wipe out all by themselves, and it's quite possible to hit your head on concrete o

Not all bike accidents involve cars. Sometimes people hit rough pavement and wipe out all by themselves, and it's quite possible to hit your head on concrete or asphalt when this happens. Humans didn't evolve to handle hitting their heads on rock-hard surfaces at high speeds; we evolved to walk around at very low speeds, and not generally fall in a way to hit our heads on things (because primitive humans were walking, not riding mechanical wheeled contraptions that kept their legs trapped).