You only need to grade-separate the crossings. There are plenty of examples of pedestrian overpasses for busy streets. You can get around a big area in lot of major cities without ever crossing a street at surface-level, but as already mentioned, it is expensive.
(Though I can't imagine people being happy about going up and down stairs, escalators, or elevators every time they want to cross a street.)
The necessity arises from the car-drivers, so you charge them for the pedestrian safety measures, just like you charge them for the creation and maintenance of limited-access highways.
Without crosswalks, there is no pedestrian-crossing phase needed in the traffic signals, so separating the two types of traffic simultaneously makes cars faster and pedestrians safer. The question really is how much drivers would be willing to pay to shave that last minute off their commute.
If you look at projects like Boston's "Big Dig", the answer is that they are willing to spend quite a lot [of other people's money].
(Though I can't imagine people being happy about going up and down stairs, escalators, or elevators every time they want to cross a street.)
The necessity arises from the car-drivers, so you charge them for the pedestrian safety measures, just like you charge them for the creation and maintenance of limited-access highways.
Without crosswalks, there is no pedestrian-crossing phase needed in the traffic signals, so separating the two types of traffic simultaneously makes cars faster and pedestrians safer. The question really is how much drivers would be willing to pay to shave that last minute off their commute.
If you look at projects like Boston's "Big Dig", the answer is that they are willing to spend quite a lot [of other people's money].