legal speed limit; statutory speed limit
Refers to the default speed limit set by law when no specific speed sign is posted. In Japan, typically 60 km/h on ordinary roads and 100 km/h on expressways.
The legal speed limit on this road is 60 km/h.
On expressways, the statutory speed limit is set at 100 km/h.
制限速度 is a broader term for any posted or regulated speed limit, while 法定速度 specifically refers to the default legal speed limit in the absence of signs.
Compound of 法定 (legal, statutory) and 速度 (speed).