The term is amorphous and vague, but Oxford's forthcoming redevelopments at the Plain roundabout and Frideswide Square continue to follow some kind of "shared space" ideology. So it's interesting to look at how previous incarnations of that have worked for cyclists. So Cowley Rd, and in particular the retail/commercial section.
I have only been in Oxford for five years, so I have no experience of Cowley Rd before the redevelopment in 2007. But here, as elsewhere, what "shared space" seems to have meant is "divide the space up between motor vehicles and pedestrians, giving the latter priority on informal crossings; ignore cyclists completely and leave them to scramble for whatever crumbs they can find". (Thankfully it didn't, in this case, involve removing all signalised crossings and forcing pedestrians to interact with the buses and trucks.) The Cowley Rd implementation seems to have involved widening the footpath and narrowing the carriageway, removing some of the on-street parking, and making crossing easier for pedestrians by prioritising traffic lights and adding regular unsignalled crossing points. The only provision for people on bicycles, at least in the central area (there are half-hearted attempts at cycle lanes on either side of that) consists of some green bike symbols painted in the middle of the carriageway and a little bit of bike parking.
Now Cowley Rd is pretty good for pedestrians — and I have used it both by myself (as an able-bodied adult), pushing a stroller, and with a toddler walking next to me. It's not comfortable crossing everywhere (as it would be in a low traffic "nearly car free" area), but the timing on the key traffic lights outside Tesco is pedestrian-friendly and there are plenty of other crossing points. The footpaths are also comfortably wide. And as a motorist (contrary to some people's assumptions I do drive reasonably regularly) Cowley Rd is often unpleasant but no worse than the other Oxford arterials. (There's a certain amount of arbitrage involved here, of course: if Cowley Rd did get much worse than Iffley Rd, some motorists would switch routes.) This section carries around 10,000 motor vehicle movements a day, including a large number of buses, but even in peak hour traffic normally does keep moving, albeit painfully slowly and in fits and starts.
But for people cycling the experience ranges from the unpleasant to the downright hostile. If the traffic is moving freely, the cars and buses speed up, pushing cyclists to the side of the road where (because the carriageway is so narrow) close passes are often unavoidable and there are risks from car doors, pedestrians, and street furnishings. Alternatively, when the traffic is stalled in peak hour, cyclists end up filtering down very narrow gaps, subject to danger as vehicles stop and start.
I am one of the few people who cycle along Cowley Rd much as the planners seem to have expected. I ride right over the top of the (now faded) green cycle symbols, go faster than I'd otherwise like to if necessary to try to hold a place in the centre of the lane, and only reluctantly filter in traffic congestion. But I'm not even remotely fit enough to sit in 20mph traffic and will give way to impatient vehicles, and I'm in a tiny minority in any event, with well over 90% of cyclists hugging the kerb regardless of the traffic situation.
(Yes, it's possible to avoid much of this section of Cowley Rd by using e.g. Howard/Catherine/Hurst/James Sts as a bypass. This can be a pretty roundabout route if you're commuting, however, and doesn't help if you're trying to get to destinations on or across Cowley Rd itself. I don't think the cyclists currently using the road are unaware of the alternatives.)
There are a lot of constraints on Cowley Rd — the density of buses, most obviously, as well as the available width — but if we acknowledge that cycling in Oxford is a major transport mode and give it proper recognition as such, surely we can claim more for it than a few bits of green paint. And the current layout is clearly not working as intended: most cyclists ignore the painted bicycle symbols completely and I've been honked at while right on top of them.
In any event, Cowley Rd illustrates that dropping the speed limit to 20mph, narrowing the carriageway and painting a few symbols on the road is not enough to turn even a small fraction of the people who currently cycle around Oxford, let alone everyone who might want to, into vehicular cyclists happy to be mixed in with dense traffic. Nor will any amount of education and assertiveness training and encouragement convince people to ride as if they were cars and take on the buses and trucks. If Oxford is going to support genuine mass cycling, to be a city where cycling to the shops is an option for everyone, Cowley Rd — along with Frideswide Square and the Plain — needs to be negotiable by people who currently don't go anywhere near it — by parents cycling with children, by older children cycling independently, and by adults who are less confident, either because they wobble a bit or are unfit, or because they lack the social confidence to face down trucks and buses.