Within cities, the curbside lane should be built wide enough for both cars and bicycles to co-exist peacefully. There don't need to be lines and markings etc., just a road width that is about 3 feet wider than "normal".

Outside cities, almost all roads should have a shoulder. Perhaps a narrow 1 foot shoulder for quieter C roads, maybe a 3 foot shoulder for somewhat busier B roads, and something 6 feet to "normal" lane width on main A roads/highways. This could, of course, depend a bit on traffic volume. If you've got a C road with a high traffic volume, then a 3 foot shoulder might be a better choice for that road. So perhaps a formula could be used which takes into account the designation of the road and the traffic volume. Nevertheless, ideally, there would be some sort of shoulder on all roads designated C, B, or A. Main arterial roads and bridges within cities should also have shoulders.

And then ... there could also be separated bicycle paths here and there as desired by the community. They would, preferably, not be placed next to a road, they would not run along side a road like a sidewalk/footpath does ... instead they would, for the most part, be hidden from view of the road. These separated bicycle paths could run along river/ocean/lake foreshores, through and around parks, to various attractions around the city, and out into the country, following old railway lines, running through various scenic spots, to neighbouring towns and other country attractions.