Every time a person riding a bike is knocked off, seriously injured, or killed, by another person driving an automobile, the first thing the police and press seem to comment on is whether the person riding the bike was wearing a helmet or not. Whether they did or not is largely irrelevant to the cause of the collision which must always be the focus of such reports! The helmets (apart from the prototype automobile deflection shield equipped one pictured above) have zero ability to prevent a collision.
In instances where a person driving hits someone riding a bike with their car, it is not the car that caused the collision. Only if the car is faulty (which technically is still the owners fault) or until such time as psychotic self driving cars are a thing, could we reasonably say the bike rider was hit by a car. Doing so in most instances shifts the blame away from the driver, which is where it almost always lies with. Whether distracted or careless, only bad driving leads to collisions, and only drivers can prevent the collisions by driving more carefully.
Helmets do nothing more than provide a slight reduction in head injuries in the event of a collision where you hit your head. Not always helpful when you've just been struck by a two tonne metal box moving at 50+ km/h.
What works better than helmets to increase the safety of those riding bikes? The best way to reduce the likelihood of collisions between vehicles and cyclists is to remove the risk and that is done by separating vehicles and cyclists. Hazard elimination is most effective as shown in the graphic below.
While I was developing that prototype helmet above, it got me thinking that our signs are not helpful. The sign below is commonly used to indicate that drivers and cyclists must share the road where there is no bicycle infrastcrture. The true intention of the signs is to indicate to drivers that there may be cyclists on the road, not even that they must share it. But the sign shows the car within inches of the person riding.
This sign essentially says to drivers its OK to squeeze by people riding bikes. Its not OK, in fact passing this close is a pretty horrible experience.
Maybe we need to change the sign to something more like this...
Or better yet, build separate and protected bike infrastructure so that the possibility of coming into conflict is greatly reduced, it gets more people riding a bike and thus drivers become more aware of people on bikes.
For the record, in BC at least, you must leave at least 1m of space. Many other jurisdictions recommend 1.5m, more is always more comfortable. Importantly, drivers are allowed to cross the centre line to overtake, in my experience some drivers seem to have a real issue using the other side of the road, even if there is no oncoming traffic.