"According to research performed by the Japan Mini Vehicles Association, there are now 51 Kei cars for every 100 households in Japan....advantages of this class of car as potential reasons for the increase - they're taxed and insured at a low rate relative to normal cars, and cheaper to maintain. I'd add that they also cost less to purchase, are generally fuel-efficient, and are much easier to park and maneuver around cramped Japanese roads."
Source: Kei cars make their way to half of Japanese households
August 17 2012
JCarBlog
http://www.jcarblog.com/2012/08/17/kei-cars-make-their-way-to-half-of-japanese-households/