The measure is aimed at reducing accidents in urban areas with heavy pedestrian traffic and narrow streets, marking a major shift in the country’s traffic rules as these roads account for around 70% of all ordinary roads nationwide.
[...] above [30 kph] the risk of pedestrians suffering fatal injuries in accidents is said to spike.
[...]
The aim of the speed limit change “is to prevent accidents by stopping dangerous driving, such as failing to slow down even on busy streets”
Yeah but it's Japan. So, in my experience at least, if driers can see pedestrians they're not driving that fast at all. It would be dishonourable 😄 but seriously, they're driving carefully.