The vowel in the first syllable of closing might be pronounced in three ways:
- [əʊ] : the old-fashioned, traditional RP British way
- [oʊ] : with some diphthongal movement, but not very much; a bit like how Americans would pronounce it
- [o:] : a long monophthong, which sounds very Singaporean
Unlike the careful enunciation of 'next station', which I argued enhances intelligibility, I see no value in using [əʊ] for closing. It seems to me that either [oʊ] or [o:] would be far more appropriate in the context of Singapore.
One other thing that surprised me is that the hyper-correct pronunciation of closing occurs in the utterance 'Doors closing' (in which there is no article and no auxiliary verb ― it would be rather more standard to say 'The doors are closing'). The use of a very careful pronunciation of closing in this abbreviated utterance with non-standard grammar sounds rather strange to me.