We don't need to come up with solutions. Countries around the world have already. Some of the larger cities in the USA have started making these changes and seeing results.
The solutions don't need to be comprehensive. While an accepted comprehensive plan maybe nice it does put all the planning up front and makes the projects take a very long time. Doing small things that push people to take other transport options doesn't need to take forever. As many cities demonstrated during the pandemic.
In the USA I think the biggest issue will be political will. But the one thing I'd like to see take off is cities removing parking minimums for new businesses or construction. The minimums were arbitrarily set and stop people from building small businesses. The parking minimums spread things out and drive the need to do something other than walk. Strong Towns has a video on it that does a better job than I can.
In short I believe comprehensive guide to being to reduce cars in cities exist at this point.