You’re right. Those homeless people living in their cars are definitely at risk.
50 (micro sieverts/ hour) * 0.5 (hours) * 251 (days) = 6275 microsieverts for work commuting.
Add in more for non-work travel time.
60% of car drivers, on the other hand, need less
than 30 minutes to commute to work/school. Also commuters taking the
bus do not travel as long as train riders: for 70% of them it takes
less than an hour to commute one way. Almost 7% of people from the
countryside indicated to commute for over two hours per direction and
day. The same group makes up only 2% among people from cities.?
Japan Guide: October 2000
http://www.japan-guide.com/topic/0011.html
Japan has a 5 day work week and 10 legal holidays/mandatory leave days per year.
Inside your house ?