Express way within Tokyo Metropolitan area (首都高速) has speed limit of 60 km/hr. or 37 mph. Yes, it is toll express way but speed limit is that slow within Tokyo.

Other parts of express way in Japan has standard speed limit of 100 km/hr. or 62 mph. Hill or curve area of express way can have speed limit reduced to 80 km/hr. or 50 mph.

Whether Japanese drivers follow the speed limit or not are totally different topic.