* Citation needed
I mean, you would expect some improvement, but (as a Dutch citizen), i expect it to prevent harm in the same way wearing helmet during sex would prevent harm.
In general: if you taking those kind of risks (as a car, as a bike, etc.) that people on a bike need a helmet, you don't belong in traffic here. The effect on mentality may be as important, if not more important.
Also, interesting to realize, if car and a bike have an accident, by law, it is automatically the fault of the car, no matter what. Even if the person on the bike is drunk, driving in the wrong direction, etc.
So, although bikers are betting their life going out, cars are betting their wealth, money and freedom.
It turns out, instead of focusing on 'who is at fault' and 'who is right', it is much safer to focus on 'lets make sure we don't hit each other' and turn accidents into a mutually-assured-destruction kind of deal. This way, every actor in traffic has a natural tendency to compensates for mistakes of the other actors. And this attitude is the one that prevents most accidents.
Both drivers and cyclists seem to believe this, but it is an exaggeration. The law says a court may decide to hold your (mandatory) liability insurance liable for some of the damage 'without having to prove your guilt'. It does not say you get the blame no matter what the pedestrian or cyclist does. At the same time, you can still sue the cyclist or pedestrian for damage to your car.
http://www.anwb.nl/juridisch-advies/aanrijding-en-dan/aanspr...
I wonder how much safer this misbelief is making us though.
Isn't this because the motorist has insurance while a bike rider does not? I've never seen cyclist insurance, although maybe the Dutch have it? There's no point trying to get blood from a stone by assigning blame to the uninsured party.
But more relevant to the Dutch situation: https://vvn.nl/dossier/fietshelm http://www.fietsersbond.nl/de-feiten/verkeer-en-veiligheid/f...
The main takeaway is that nobody in Netherland wants helmets to be mandatory. The positive effects of a helmet are insufficiently proven, and the negative effects of making helmets mandatory seem not worth the risk. Some organizations do recommend helmets for children between 10 and 14, which seems to be the group that's most likely to benefit from them.