I'm having a lot of trouble trying to conceptualize how "car/bike traffic" could be a giffen good. "A product that people consume more of as the price rises". Raising/creating tolls for cars decreases usage. Raising bus prices also discourages use. Could you help clarify what you meant?
As for road space usage, generally bike lanes are added by adjusting street parking, narrowing lanes, etc. Eg I worked on a recent project where two 4m lanes were turned into a 3m middle lane and 3.5m curb lane and a 0.5m buffer and a 1.0m bike lane. I can't think of many situations where bike lanes were added by removing capacity from roads that had usage approaching capacity.
London’s Embankment from Westminster to Blackfriars (and the rest of CS3 on other roads) added a bike lane by removing car capacity despite it being full every rush hour. The road as a whole has higher throughput now.
Oh, I recently rode through there the other day for the first time as I went from East London to Hyde Park! It was really nice to have a dedicated cycle way like that.
As for road space usage, generally bike lanes are added by adjusting street parking, narrowing lanes, etc. Eg I worked on a recent project where two 4m lanes were turned into a 3m middle lane and 3.5m curb lane and a 0.5m buffer and a 1.0m bike lane. I can't think of many situations where bike lanes were added by removing capacity from roads that had usage approaching capacity.