Napier to Wellington
You want to take highway 50 and then it joins highway 2 from Takapau, then stay on highway 2 all the way.
Chances are your GPS or GoogleMaps will both show you to take Highway 2 from Napier and then turn off highway 2 at Woodville towards Palmerston North and highway 57 then highway 1. Don’t do this, its not much faster, the roads are less fun and there are more people on this route plus more trucks.
Highway 50 is almost empty every time I’ve been on it other than a few farmers at times and has some nice corners as well and then highway 2 south of Woodville is much less busy than cutting across to highway 1 and then you get a Mountain road to finish on your way into Wellington via highway 2 rather than just a motorway on highway 1. I’ve attached the GoogleMaps pin you need to drop to get it to offer you this route and as you can see its not much slower.