State Road A1A begins in Fernandina Beach on the St. Marys river and extends south 390 miles to Miami. Many of the towns along the way are famous for their laid back beach culture.
It is the main route through most towns on the Atlantic Ocean.
U.S. Highway 1 comes into Florida across the Georgia border on the St. Marys River near Boulougne, and extends 547 miles to Key West.
A1A is the beach highway, while US-1 goes through older towns that followed the extension of the railroad down the state in the 1800s and 1900s.
In the days before interstate highways, U.S.-1 was the main corridor carrying motorists from New England and other northern and mid-Atlantic states down into Florida.
When State Road A1A comes to inlets or other barriers, it sometimes jogs back and forth across the Intracoastal Waterway to join US-1, but generally you will be near the ocean on the entire length of both these roads.
US-1 and SR-A1A parallel the route of Interstate 95.
You can take I-95 all the way to Miami where you hit US-1 that takes you to the Keys. But that's no fun. Take a day or two more and enjoy the towns along the way.