I think this question illustrates why deciding these kinds of things on a referendum type basis is hardly ideal.
It's difficult to decide just who is affected by a measure like this - just the people within the zone, the people just outside the zone, the people commuting in from a fair distance away (some of whom will come by car and some by public transport) ... and how do you balance each of these groups views against one another - should the vote be weighed more in favour of one area than another... and so on.
Really, deciding transport policy in a piecemeal way like this, area by area, is silly. The clue is in the word "transport" surely; the nature of transport is that it links places together and each link in the chain doesn't just affect the area it passes through.
We ought to have a strong and consistent transport policy set by central government that is applied across the country in an integrated fashion. This is what London manages to do within its boundaries; a travelcard for example works on trains, buses, tubes, trams, the lot.
Wouldn't it be nice if we had something like the oyster card that worked nationwide? So if I went to another UK city I wouldn't have to spend half an hour working out how the local PT ticketing system works before I could go anywhere.
Countries like Germany or the Netherlands manage to run something approaching a fully integrated transport system. Why can't we just sort it out?! People going on about how it would only work if we renationalised everything therefore it will never happen - that's a complete red herring. London, and other European countries prove that private operators can run a perfectly good service as long as they are effectively regulated and co-ordinated by a central, public body.
I don't know what it is with people in this country, that makes them so apathetic and unwilling to consider investing in alternatives to the private car, as demonstrated by the folk of Manchester. Germans love their cars too... but somehow they manage to do that at the same time as running one of the best public transport systems there is.
Perhaps it's the London brain-drain effect, leaving the rest of the country populated by nothing but numpties.