It's useless to build a straight road, 4 wide lanes, then stick a sign on the side going "pls no speederino". The roads and the streets themselves need to be designed so that they do not allow unsafe use. Meaning any road/street shared by pedestrians needs to have narrow lanes, few lanes, sidewalks separated by e.g. a row of trees, speed bumps and raised crosswalks, bollards separating lanes, chicanes, etc.
That's already the norm in the UK. To be honest I'd forgotten many residential roads in the US were dual cartridge ways. That does make things more tricky.
