score:4
Those lines are used before/on curves, as well as straightaways that should be taken at slower speeds, to help slow down the driver. By having dotted lines, it makes the drivers feel they are going too fast and makes the lanes feel more cramped, coercing them to slow down.
There is no defined rule on this, which is why you can't find information on official sites. It's something each prefecture adds on their discretion.
I've confirmed these by looking through some driving sites. (Here and here)