People in Amsterdam use km/h not mph.
From my experience in france, on 30km/h roads, people would drive anywhere between 30-40km/h, while on 50km/h roads, people would drive between 50 and 55km/h.
I was just confused by the usage of mph in this context and interpreted parent's comment in a way that would mean amsterdam residents were using mph.
I also wanted to provide a data point that does indeed go in the way of the parent regarding people going over the speed limit.