It's both north and east. And I think that was the point of the article, that New England has it particularly bad for this.
Most people think that east coast cities are on a north-south axis, but as you go up I-95 (the major highway connecting these cities) you are actually traveling northeast. It was a head trip for me being from DC when I realized I could drive straight north for 5 hours and end up in Rochester, NY, or drive "north" on 95 for 5 hours and end up in New York City, but the distance between those two points was also itself a 5-6 hour drive.
Also the article says Massachusetts wouldn't do it without the rest of New England also joining:
> A majority of other states in New England would have to jump on the time-zone train, too.
Edit: Must have been downvoted by west coasters who don't know what new england is ...