Comment by smileysteve

The bright side of roundabouts and (curbs) annd curves is that they create better (more cautious, observing) drivers, with minor consequences (like hitting a curb).

For lowering the high speed, we can also stack roundabouts, curbs (ie diverge and coverage the road).

The other positive of raised curbs is that we can add shrubbery as a natural traffic barrier, and there are some nice safety impacts from this too, such as reduced road runoff / flash flooding - and environmental factors like shade and cooling.