In urban areas that are already dense this can be done without any significant infrastructue investments by simply changing how the traffic patterns work on existing roads.
A good example of this is Barcelona's "superblocks": https://www.vox.com/energy-and-environment/2019/4/9/18300797...
If we start today and incorporate the lessons they've learned, it hopefully won't take us 60 years to get there.
The principle is simple: In designated spots, prevent through traffic for cars while allowing bicycles to go through. This massively reduces car traffic on those streets. In Ghent they did that by simply placing obstructions on the road that only bicycles can maneuver around. Once more people are cycling, you'll have increased political will to spend money on more ambitious infrastructure such as in Amsterdam.
Having lived and cycled in Amsterdam to me it did seem like a major investment. Sure if one were to design a greenfield city then it’s not a big deal. But to pivot a car centric city to safely accommodate cyclists is a major change. The city residents have to go through the transition process which isn’t going to be fun.
I’ve seen it done half ass way in India and US which end up being deadly for cyclists.
I am all for cycling, I absolutely loved my two year stint at Amsterdam. It’s a life changing experience. But let’s not underestimate the costs involved in transition. Also, the city residents have to be onboard with the process, as they are the biggest stakeholders. Otherwise the implementation will get dumped half way through with disastrous results.