No worry, you can also use Street-view,
so you can understand about which type roads are using lower limit speed.
This is the same way in every country.
In the residential area, near the elementary schools and parks,
the sections with many signals even in the city, continuous curves, slopes,
tunnels and strong wind and deep foggy sections are less than 40km/h limit usual.
50km/h limit is safer and wider with many heavy-duty trucks
also few pedestrians and bicycles out of urban towns area,
60km/h limit is mostly case without a speed limit sign(as plate), more safer than 50.
There are many sections with 60 or 80km/h limit on express-ways (main lanes) and other toll roads.
http://en.driveplaza.com/rules/rules.htmlEven no charge roads excluding small motorcycles 125cc or less and
small-sized special motor vehicles like these, of course including pedestrians and bicycles,
http://www.city.ama.aichi.jp/zeikin/keijidousya/005244.htmlmore than 60km/h limit roads exist, but there are not so many.
@ Paul
Only about speed traps :
Although that knowledge is not a wrong, but a bit not enough,
means using their devices are not only that portable type.
and it will be updated to a new style soon, I do not explain about it, though.
Speed and other traffic violations spots are roughly decided, only local drivers know well.