Since I read more of their proposal and now see that they're proposing doubling the size of the Hawke's Bay Expressway to four lanes I have more thoughts.

Firstly, given the expressway goes over two major rivers with high stopbanks, that means two bridges somehow either expanded or additional bridges built, or the bridges replaced - none of which is cheap.

The expressway between the Ngaruroro and Tutaekuri is already susceptible to being blocked by flooding as there are two streams that go under it at low points. Even after Gabrielle those points have had water encroach upon the road so doubling the length of those culverts probably also means doubling their capacity as well - or, a more resilient solution might be to raise the height of the road entirely on an elevated causeway given we know the flood plain between those two rivers is where the water goes in historical floods that breach stopbanks.

Outside of local freight traffic the bulk of the volume is rush-hour transfers of vehicles from either of the two cities as people go to work. A lot of that traffic is stuff like sparkies, plumbers etc who can't mode shift - but there is still a volume of traffic that could be moved by public transport. A fast and regular railcar service between Waipukurau and the Airport could make a lot of sense.

The other thing we really need to do is to shift long distance freight off the roads altogether - the two north of the expressway are far too prone to closure - and even SH2 south got closed during Gabrielle. As much as i'd love it to be trains its probably better for that traffic to be both coastal shipping and train - and a lot already is (ie logs shipping internationally direct from Napier port).

In any case, my opinion is that 4 lanes on the expressway is 150% more capacity than it needs 95% of the time, and would most likely just shift the congestion point from around the Tutaekuri bridge south of the Taradale on ramps to somewhere else. The problem isn't even really the road's capacity.

As the hand-drawn sign at Taradale says (I paraphrase) "Merge like a Zip, not f$%king Velcro".