Known and well-signposted speed camera on dangerous turns, close to schools or kindergartens would vastly improve street safety.

Unfortunately most German(!) street cameras are placed to surprise the driver, causing nearly continuous disruption even for those who don't speed. Their destabilizing effect on traffic can be observed quite easily as people suddenly brake, make light signs to warn others, surprisingly change lanes (because of the sudden speed reduction), etc.

This is because in Germany the money goes to the local authorities.

It doesn't help that placing and maintaining them is pretty expensive (and often outsourced with profit-sharing). Local authorities and private partners have little incentive to reduce their income per device just to increase road safety.