What route would you travel between the northernmost and southermost city

US route 1 or US highway from north to south

Explanation:

This is a major north-south U. S. Highway that runs from Key West, Florida north to Fort Kent, Maine, at the Canada-US border, making it the longest north-south road in the United States.

The highway connects most of the major cities of the East Coast including Miami, Jacksonville, Richmond, Washington, D. C., Baltimore, Philadelphia, New York City, Boston and Portland, passing from the Southeastern United States to New England.