I'm quite sure that the primary factor for safety in the Netherlands is the excellent infrastructure. Separate bike lanes, crossings that take into account viewing angles, etc. - cyclist safety is so ingrained in road design here, and it directly affects how safe it is to cycle, even when you're a lone cyclist.
The law is probably a second large factor, and only then do I think the number of cyclists comes into play. And even then, that sheer number has only been achieved thanks to the former two factors - I'm confident that that has played a far greater role than helmets being optional.
From personal experience I agree. Let me tell you HN folks a small story. There are a few parts in Amsterdam that I feel that are inherently unsafe. I avoid those places and cycle 100 meters extra. Let me see if I can find a Google Maps image as an example.
Yes! Found it! [1]
Why this place is dangerous: tram rails to get your bike wheel stuck in on the left. Cars on the right. Especially on a rainy day with lots of traffic this place is scary. It's quite easy to get stuck in a tram rail with cars behind you. The lane that cyclists seem to cycle in is mostly between the first tram rail and the cars on the right (see [2] for a better perspective of it). Whenever I cycle this small part, I always hope that every parked driver knows the Dutch reach. Amsterdam is a multicultural city with expats, so I'm always a bit weary whenever I forgot to choose the safer option. Up until now, they fortunately all did [3].
I've been there, and during wet weather, I've once felt my rear wheel start to slip on a tram rail (fortunately I managed to compensate). I learned to take tram rails at a steeper angle, which has served me well. Never had any other trouble here, but yes, I watch the car doors. Or I ride between the tram rails, because there's no way cars will be going very fast here.
Still, it's clearly a place that lacks the separate bike lanes that are so common elsewhere.
As somebody who cycled in nearly 15 different nations inside and outside of Europe, cycling in the Netherlands is a joy. For me it was mainly three factors:
1. Infrastructure: wide enough seperated lanes without potholes in a bright color, making it clear also to pedestrians. Most of the time very clear visibility on crossroads.
2. Motorized traffic is most of the time far less stressed than in other parts of europe
3. Other cyclists seem to be more educated about traffic rules than in other places where you often only have two types: the suicidal and the overly cautionous, barly going faster than a pedestrian
> Other cyclists seem to be more educated about traffic rules than in other places where you often only have two types: the suicidal and the overly cautionous, barly going faster than a pedestrian
We also have those types (the overly cautious ones are generally tourists, often in large groups), but we have a couple of other types to balance things out.
Worst examples of suicidal: a cyclist running a red light on the most dangerous intersection of the city while on the phone and not remotely paying attention to traffic. Or parents teaching their young kids to lane-split against motorised traffic.
The law is probably a second large factor, and only then do I think the number of cyclists comes into play. And even then, that sheer number has only been achieved thanks to the former two factors - I'm confident that that has played a far greater role than helmets being optional.