I actually know nothing of highways. ;) I was 17 when I made my first (and sadly last so far) trip to Massachusetts (well, and the USA in general, I have to say) and I wasn´t allowed to drive then (as you don´t get your driver´s license before 18 here in Germany). So highways don´t mean much to me as it was other people taking me from one point to the next.
As far as I remember the only sea town I visited was Cape Cod but then that´s 19 years ago by now and my memory has faded a lot.