Trying to prevent injury/death in case of a car hitting a cyclists is the wrong approach. What needs to be prevented is the car hitting the cyclist.
Decades of research and practical experience in more cycling friendly places has shown that by far the most effective solution is separating road users that have different speeds: pedestrians (slowest), cyclists (slowish), cars & motorcycles (fast). Where they can't be separated, you take measures to reduce the speed of the faster road users so the speed difference is smaller or disappears.
Here in Canada we (mostly) separate pedestrians but for some reason not cyclists. I've never heard anyone bring up helmets when a pedestrian gets struck by a car.