The areas north of New York City were not immune to cancellations of planned expressways.
https://www.google.com/maps/d/edit?mid=1tGEXAbQp0DQ3V7LNtzMjRgttkJNbAAqg&usp=sharing
The most famous was the Hudson River Expressway, to go from The Bronx to Beacon, near Newburgh. Parts of it were to be built on landfill, extending as much as 1300 feet into the Hudson River. The thought of the pristine Hudson Valley being ruined with the sounds of trucks and buses gave pause. All that was built was an expressway from Crotonville to Peekskill.
If the highway planners had their way, Peekskill would've been the crossroads for 3 different expressways, the aforementioned Hudson River Expressway, along with roads to Brewster and to South Salem (and possibly New Haven).
http://www.nycroads.com/roads/unbuilt_hudson/
I agree with the Hudson River Expressway north of I-287 but why did planners even include I-487 (HRE) south of Tarrytown? Seems like an nonstarter to cut through the riverfront in Southern Westchester.
Regardless, seems to me if they made the route more inland north of I-287 they might have gotten it through. It's a shame, because it's a sorely needed link. The TSP has been made a freeway because of this and trucks aren't even allowed on it.
The Bear Mountain Parkway is another one that only has a short section to complete it.