[gibolt]

Not 1/2, closer to 1/10 (for the exact space of the car). Cars also need far more buffer space, parking space, overall road area for maneuvering around a city. If completely replaced, infrastructure area could probably be reduced by ~20-100x

[xracy]

I'm being real generous here that on a 4 lane road, if you want to add bikes I would just take away 1 lane of car traffic, and that would allow for bikes to be insulated from the cars in both directions.

But I definitely agree with you that we could probably 1/100th the size of roads (and open up a whole lot of space for property development), if everyone biked everywhere. (Not useful as a goal, just useful as an idea for space requirements.)