Pronunciation of "轧" in 富顺(县)?
A tentative hypothesis:

It seems like there is a 挖 vs 蛙 split, which the dictionary has tried to notate. There is some kind of difference between the /w/ of 挖 and /ʋ/ of 蛙.

The fortition of /w/ to [ʋ] is attested across all of northern Mandarin, and is particularly prevalent in Beijing and the Northeast. This dictionary seems to suggest that this process is incomplete.

I think that the pinyin orthography used by the book has "w" representing /ʋ/, and the "o" representing /w/ instead.

My evidence for this is 娃儿 being transcribed as "wáer (连读)" whilst still having 轧 as "ōā (连读)" in the dictionary.