The Netherlands did it over the course of a few decades, probably less than 20 years. You'd be surprised how fast things go since bicycle infrastructure is so dirt cheap in comparison to car infrastructure.

The next point is that what you're saying is what you've been doing for decades, but nobody goes and actually fixes the issues at hand. I think it's a cultural difference there too; in the Netherlands they constantly upgrade and change their infrastructure to make it all better whereas in the US, well, once a road is there it'll better stay there for the next 50 years or so or maybe we'll patch a little.

They continously monitor all roads as well. If an intersection has more accidents than normal, it gets scrapped, redesigned and rebuilt safer. Usually it gets upgraded to much safer roundabout. Speeds get lowered. In Canada or the US you'll be lucky if a stop sign is placed, wow!

In my town in the Netherlands they lowered speeds throughout the city to from 50 to 30 kph, about 20mph. With most interactions now being roundabouts though, I can move faster there by car than I can here at home in Vancouver where speeds vary between 50 and 80 and mostly stopping at stop signs and traffic lights. Hell, anything under 5 miles, 8 kilometers, I can do faster by bike in the Netherlands than by car here in Canada. The Netherlands does what works.

If you keep placing speed bumps, you'll never get anywhere.