
So what exactly is Shared Space? The principle is quite simple and appealing. All road users share the same space on the street on equal terms and with no priority given to one direction of travel over another (although the drive-on-the-left convention would continue to apply) or to vehicles over pedestrians. So no pavement / road distinction, no traffic signals or give way markings at junctions and no specific pedestrian crossings (since pedestrians can freely cross anywhere, almost as if the whole street were a zebra crossing).
Of course such sharing is only possible at very low speeds, perhaps around 10 mph, and with limited vehicular traffic volumes, especially through traffic. We already have examples in the form of Home Zones, based on the Dutch Woonerf principle, but these have little if any through traffic so cannot be taken as models for how the concept might work on busy streets like Park Street. The forecourt of Temple Meads station is cited as an example of shared space, but it still has separate pavements and of course no through traffic since all vehicles using that space are accessing the station.

Ashford before....
There are some examples in the UK, notable Ashford in Kent where the former ring road has been downgraded to what is claimed to be Shared Space and the results certainly look attractive in still pictures compared to what went before, as described in this post by Tom Vandebilt and as shown above (before) and below (after) here. However it's clear that this isn't pure Shared Space but retains some segregation and priority, notably keeping separate pavement and road (technically footway and carriageway).

.....Ashford after.
I expect that what we might get in Bristol will also be some kind of hybrid, or bastard child perhaps. Neither one thing nor the other, rather like what was done in the Centre ten years ago. Therein lies a danger. We may end up with something which confuses the existing conventions without giving clear guidance as to what replaces them. The Centre has been a road safety disaster with 6 pedestrian deaths in a few years at just a couple of crossing points for precisely that reason.
There is very little practical experience of Shared Space in the UK and virtually none in Bristol, so it is easy to think that Shared Space will be some sort of panacea. But experience elsewhere suggests that results will be mixed at best. Recorded injury accidents may fall but what about low level harassment and intimidation which is not recorded or even acknowledged by the authorities? Such conflict could even become worse as measures that give some priority or protection to pedestrians and cyclists are removed.
I've no doubt that we need to change the conventions of how streets are used by traffic and to change the visual character of our streets so they look like sociable places. But I believe such change must be based on a deeper understanding of the nature of conflict between different road users which does not yet appear to exist amongst the highway engineers who will be entrusted with implementing Shared Space. So watch this, er, space.