Originally Posted by
Paul Barnard
Very simply, that is the answer. The cost would be prohibitive. In some places it's just not possible.
Unfortunately, those are nothing more than excuses. The cost per unit length for cars is many many times higher than what is required for a bicycle. So it's only political will that prevents bike lanes to be added where roads for cars are added or repaired. And it's been documented in a video by Mikael Colville-Andersen that roads for cars cost society money but lanes for bicycles earn money.