128. (1) No person shall drive a motor vehicle at a rate of speed greater than,
(a) 50 kilometres per hour on a highway within a local municipality or within a built-up area;
(b) despite clause (a), 80 kilometres per hour on a highway, not within a built-up area, that is within a local municipality
+++ This is not legal advice, only my opinion +++
I will have to dig up my notes, but I'm 90% sure.
Although, arguing what is built-up and what is not built-up might be more challenging than you think.