The top of 22 is fucked but an alternate route heading in the same direction is to pop over the top of Hunua from Clevedon (via monument rd and paparimu) to SH2, then down from Mangatawhiri to Mercer (I forget the road).
Quick jaunt down SH1 to Rangiriri then towards Glen Murray take a left down Rotongaro Rd to Hetherington Rd, right up Hetherington to SH22 where it is not too bad through to Ngaruawahia.
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