Things that have been said about cars before but I feel like saying them again
And the Japanese speed limits almost deserve their own post. The following is from wikipedia, but seemed accurate:
* speed cannot be set higher than 60 km/h for any streets with an at-grade intersection, or where pedestrians or cyclists are permitted.
* speed limits of 30 km/h on residential streets and 40 km/h are common for urban two-lane roads.
* 20km/h may be set when there are many seniors, children, narrow etc