as for your arguments about taxis causing more pollution, i'm not so sure. if i've already got a car, then for me to use a taxi to take me a few miles is indeed a nonsense. but for a substantial number of car-less people who mainly walk about town or get on a bus, then the once weekly trip from the supermarket with heavy bags or from argos with a bookcase by taxi seems to make sense. without the option of paying c.£5er for these odd journeys, they may be tempted to get a motorcar. and once they've taxed, insured and lost the depreciation on it, the mentality goes that they may as well use it every day. it's car sharing by a different name.
Good point - that cabs can allow people to go car-free more easily, not really occurred to me.
I think that it's not occurred because the majority of people that I know that are car-free either use their bikes for such journeys, use the bus, have stuff delivered, and do all of the above as a series of journeys throughout the week, thus not needing a single big shop and also cutting down on the amount of food that doesn't get eaten. But it may well be that my experiences are biased by being in a location with good public transport.
On the other hand, the people that I know that do use taxis tend to be car owners anyway, and are making a trip where they don't want to use the car (eg into city centre, home from pub, on expenses, etc) but don't want to go via public transport because it's slow, dirty, 'common', etc. YMMV.
anyway, I still don't think that they should be given the benefits of the use of bus lanes as people swapping to them wouldn't have the benefits that swapping to buses or bikes would have but would still serve to slow down those two groups and potentially put off people from the latter.
