Here's a quick article I found on the unrealisticness of the Japanese test cycle:
https://www.autoblog.com/2009/04/03/....4%20mpg%20(US)!
In the US, the 2010 Prius is rated for 48mpg highway. In Japan, it was rated for 90mpg. Japanese Prius drivers tend to get around 50mpg equivalent in real world conditions. It isn't that their version of the car is any more efficient, their test is just bogus.