Which U.S. Interstate highway runs from Miami, Florida to Houlton, Maine?

The U.S. Interstate highway running from Miami, Florida, to Houlton, Maine, is Interstate 95.

I-95 is the principal north–south Interstate on the East Coast. It begins at U.S. Route 1 in Miami and runs roughly 1,906 miles to the Houlton–Woodstock Border Crossing, where the road continues into New Brunswick as Route 95. Along the way it serves major metropolitan areas including Jacksonville, Richmond, Washington, Baltimore, Philadelphia, New York, Boston and Portland.

The highway was established in 1957 and incorporates sections of older toll roads, especially in the Northeast. For decades, a gap in central New Jersey prevented continuous I-95 travel on its original route. A connection involving the Pennsylvania Turnpike was completed on 22 September 2018, creating a continuous Interstate route between Maine and Florida.

The answer is not Interstate 5, which follows the Pacific Coast, or Interstate 75, which runs through the Great Lakes and Southeast. Interstate 85 serves a more inland route through the southeastern states. I-95 also does not end at the Canadian border in a city center: its northern terminus is at the Houlton border crossing.