One common argument is that drivers have more respect for cyclists without helmets, i.e. they're more afraid of hitting a cyclist without a helmet.
The discussion goes back a long time, this article for instance is 9.5 years old: https://www.scientificamerican.com/article/strange-but-true-...
I guess, most cyclists think it's more likely that they'll be hit by a car, not a pedestrian.
It could also be that some cyclists don't have the money to buy a helmet - or other types of safety gear.
Yet this study is cited in every discussion of bike helmet use.
I've been interested in this topic for some time, as a year round bike commuter with my entire family on bikes. It's become a prickly topic because of the intensity of advocacy from both sides of the debate.
Good maintenance, situational awareness, and defensive/evasive riding skills are all under emphasized.
A critical one is knowing how to wipe out correctly, a martial art unto itself.
As much as a boxer will instinctively react to a fist flying at his face, a cyclist should know how to respond to a sudden altercation with the pavement. Many of them don't.
I mean, if you step into the ring against a professional Boxer having no training but think a shiny new bike helmet will keep you safe, well, good luck with that.
We're slaves to measurable outcomes, and it's easy measure and gather statistics on helmets. It's harder to measure how effective a rough and tumble childhood is for avoiding concussions and other accident related injuries later in life.
Seat headrests and side impact air bags provide this function much more effectively than loose helmets. Which are not safe for use in passenger cars due to neck trauma. Further, your skull hitting the pavement is more rapid acceleration than a survivable car crash.
That said, NASCAR drivers do use helmets and a five point harness instead of air bags. But, very importantly they strap the helmet to the head rest, but that only works because of the five point harness and several other safety systems missing from consumer cars. https://en.wikipedia.org/wiki/HANS_device
TLDR: The issue is neck trauma. Which NASCAR avoids, by strapping both the driver and their helmet down.
Well, other than it being tremendously inconvenient and messing up people's hair. We have active prioritized those two things over safety.
A prevalence of biking on the sidewalk in an area is a signal to designers that cyclists feel it is too dangerous to bike on the road amongst traffic. It means that a protected bike lane needs to be built.
(Tourists tend to have bikes with bike-rental logos, or Citibikes; locals tend to have their own bikes, or if on citibikes, are dressed more like locals.)
E.g. take the first graph: the red surface starts at 0 and the upper bound is the actual 'overall ridership' for Second Avenue, right? (note to author: even when the units seem obvious to you, they might not actually be obvious for everyone). So the lower bound of the green surface (Lafayette Street) has the same shape as the data for Second Avenue. Why? What does that mean? It's just the upper bound of the green surface which is the actual data for Lafayette street, no?
On topic: glad to see bicycle usage is rising, but would be interesting to see if e.g. car usage is declining and how the total number of people on the road is changing.
Stacking those graphs in that way only is valid if there are no double-countings in the data. New York is large, but I think/guess (I know little of street layout in NY, but looking at coordinates, Layafette street at Astor plaza and Second Avenue at 7th Street seem fairly close to each other) that is unlikely.
Cyclists die in traffic because they are hit by multi-ton motorized vehicles, not any of the things enumerated here.
