I have three friends who I use as a litmus test for cycling. They don't cycle in Oxford, even though it would often be convenient for them if they did — one of them walks two miles to work instead — largely because they find the environment too hostile and unpleasant. They are all fit adults in their thirties and they all know how to cycle: one of them is a recreational mountain biker and knows more about bicycles than I do, one of them used to cycle back home in a small town in the United States, and the third has at least tried cycling here.
These friends walk almost everywhere in town, rather than driving or even catching buses, so enabling them to shift some of their trips to bicycle won't help congestion or carbon emissions or anything like that. But if we can't get people like this cycling, we have no hope of getting less fit people out of their cars, or of convincing parents to let their ten year olds cycle to school.
Doing something about the worst and least pleasant cycling bottlenecks — the Botley Rd railway bridge, the Plain, and suchlike — might get one of these three cycling. For the others, even the recently resurfaced Iffley Rd and Warneford Lane, let alone the debacle that is Cowley Rd, are just too hostile. We aren't going to make cycling accessible to everyone, or even increase the share of trips done by bike by 50%, without physically protected cycle paths along the key routes which carry fast or dense motor traffic. "Shared space" schemes like Frideswide Square and the Plain rebuild and incremental improvements to on-road cycle lanes may improve things for existing cyclists, but aren't enough to bring in the next tranche of potential cyclists, let alone the ones after that.