We are not here to "preach to the choir" regarding the more obvious aspects of bike safety such as the importance of helmets or bike lights. Rather, the post will consider Japanese traffic law as it relates to cyclists as well as the challenges and dangers posed to cyclists in Japan by road conditions and motorist behaviors.
Bicycles are considered light vehicles and are allowed on motorways, unless posted.
In principle bicycles are not allowed on sidewalks.
Bicycles must be equipped with a front light and brakes front and rear.
Japan does not have a helmet law
USA/ 677 (2011, latest year for which I could find data, down from 721 in 2001)
Japan/ 700 (approx. annual number); this figure was cited by the teacher at my school who is responsible for bike safety in a recent speech to students- 80% of the 700 students ride to school; the number was sourced to the National Police Agency
USA/ 317,000,000 (pop.)
Now, without reliable "exposure" data, these numbers may not be particularly helpful. However, based on the 30 combined years of experience Don and I have cycling in Japan, we can attest that Japanese roads and motorists offer serious challenges to cyclists' safety.
Roads are often narrow and congested, made even moreso by parked vehicles.
Bike lanes are practically nonexistent.
Japan loves tunnels, which can be quite harrowing in heavy traffic.
* drive too fast, in particular the cabbies
* ignore red lights
* overtake cyclists and abruptly turn, sometimes with no signal (called "winker" in Japan)
* pull out or turn in front of approaching cyclists, necessitating expert handling skills by the latter (in this regard, beware of other cyclists, too)
* pass too closely
* are unaware that cyclists have the right to use the road
* ride while texting (ditto the drivers and the pedestrians)
* cycle while holding an umbrella
* ride on the wrong side of the road
* take blind corners at speed
* veer into the path of an overtaking rider (pedestrians do this too)
It hardly needs saying that not all cyclists and drivers are unsafe or inconsiderate. Nevertheless, we encounter the above often enough to know the importance of unceasing vigilance and defensive cycling.
There is plenty of great cycling to be had in Japan; mostly it's far from the madding crowd.