Even with the caveats about limited data and untangling causation and correlation, the statistics are striking: the first year of a scheme in Wales where the speed limit on urban roads was lowered to 20mph resulted in about 100 fewer people killed or seriously injured.
To be fair in NL a lot of people ignore the speed limits if the road invites you to drive faster (not enough traffic calming stuff). Not a lot and still driving safely but for example there’s this huge straight road near my house that they changed to 30 recently but didn’t make any changes to the infrastructure and pretty much everyone still drives 50 on it. Also on highways it’s 100 everywhere during the day but you see a lot driving 110/120 where there’s no speed control.