As much as l am loathe to defend NH state Pols, l really don’t think theres an ulterior motive. I think NH is just still stuck in the mindset that self evidently, more lanes reduces congestion. Most of the US still thinks the same way. MassDOT is actually one of, if not the most progressive state DOT on that front, which given the proximity really highlights how behind NH is on the current traffic engineering trends.
As far as being anti rail, my sense as someone with a lot of family on the wrong side of the border is its a combination of:
thinking public transport is for the poors,
l personally won’t use it,
its expensive (but roads are free to build/maintain obviously),
seeing the MBTA as a salient of LIBERAL MA intruding into NH’s slice of Real America (TM), something something small government,
it being a physical representation of a big city (which they dislike/ are scared of), ect, ect, ect.