Earlier quoted context omitted.
> People who are likely to have crashes are likely to be able who ignore the limit. ... which is why you have to do actual road design. You can't just put up a speed sign and hope people will magically abide by it. Roads need to be designed for the speed you want people to drive. When done properly the vast majority of drivers will follow the speed limit without ever having to look at the signs, because it'll be the…
It isn't road design, it is behavioural/cultural. People will drive recklessly when they do not care, for whatever reason, about the people they may injure by doing so. That is it. If you look at comparisons between countries, it is clear that means are different.
The thing is, the vast majority of people - regardless of culture - have some basic sense of self-preservation. Speeding is easy when that 30km/h road is designed like a 120km/h highway. Speeding is a lot harder when that 30km/h road has speed bumps, chicanes, bottlenecks, and is paved with bricks rather than asphalt: if you try to speed, it'll quickly feel like you need to be a professional rally driver to keep your car under control.
Deliberately making roads "unsafe" forces people to slow down, which in turn actually makes it safe.