I think wherever possible (i.e older babies onwards) buggies should be folded up. I am so tired of these oversized contraptions being pushed through the aisles, banging passengers thighs and shoulders as the squeeze talong a narrow aisle. I have had my ankles knocked todday and somehow had to squeeze against another passenger along the crowded aisle to make room for yet another buggy.
Theworst thing I have witnesses was a wheeelchair user being denied access onto the bus because there was already a buggy in the wheelchair space. The buggy owner didn't offer to fold up and got off a few stops later.