The designation is unique: other than SR A1A (now SR 811, SR 707, SR 732, and an extension of SR 842), only two other Florida State Roads have begun with a letter: SR A19A (now a loop of SR 693-SR 699-SR 682 near St. Petersburg), and SR G1A (now SR 300) have existed.
The road was assigned the number SR 1 in the 1945 renumbering as the easternmost major north-south road. However, just across the Intracoastal Waterway, and in some cases on the same side, is U.S. Route 1 (SR 5), causing confusion. The State Road Board changed the designation to SR A1A on November 25, 1946, about a year and a half after the renumbering. SR A1A is signed north-south.
The twin A's are often said to stand for 'Atlantic 1 Alternate', but this argument fails when applied to the former A19A, a loop off US 19 near St. Petersburg, which touched the Gulf of Mexico rather than the Atlantic Ocean. On the other hand, the former SR G1A was on the Gulf.
SR A1A is heavily associated with Florida beach culture and is known for its lush subtropical scenery and ocean vistas. In many places, the highway directly fronts the Atlantic Ocean, and in other places, runs 1-5 blocks inland from the beachfront. For most of its length, A1A runs along Florida's East Coast Barrier Islands, separated from the mainland of the state by the Intracoastal Waterway. Because of the road's proximity to the ocean and its susceptibility to storm surges, sections of A1A are often closed or even minorly damaged by hurricanes and tropical storms. North of Atlantic Beach, however, A1A turns inland for several blocks before resuming a northward course that ends at the St. John's River. A ferry takes vehicular traffic to the northern section of A1A which continues inland toward Callahan.
Two miles of A1A were used as part of the legendary Daytona Beach Road Course. A1A also has been a backbone of Florida Spring Break, serving as "the strip" in both Fort Lauderdale, a popular spring break destination in the 60s, 70s, and 80s, as well as Daytona Beach, which became a popular destination for college spring breakers in the 80s through the present. In Miami Beach, A1A serves as Collins Avenue, one of the city's main North-South thoroughfares, and travels a similar route through exclusive Palm Beach, further to the north. A1A also bridges Sebastian Inlet near Vero Beach, known as the Surf Capital of the East Coast, and passes just to the west of Cape Canaveral and the Kennedy Space Center. A1A also passes through St. Augustine, the oldest city in the United States.
SR A1A begins as a 2 lane, then 4 lane route along the Straits of Florida. Running along the south shore of Key West, SR A1A is the southernmost numbered highway in the lower 48 states. The portion in Monroe County is secretly known as US A1A. Next, it passes East Martello Tower and Key West International Airport. SR A1A curves to the north to end at U.S. Route 1 (SR 5), after intersecting with SR 5A. SR A1A ends, but begins again at I-395 and US 1 in Miami.
Prior to the 1945 renumbering, the route that became SR 1 had the following numbers:
| County | Location | Mile | Destinations | Notes |
|---|---|---|---|---|
| Southern terminus | ||||
| Monroe | Key West | 0 | Bertha Street | Also South Roosevelt Boulevard |
| 3 | ||||
| Discontinuous section in highway | ||||
| Miami-Dade | Miami | Also the MacArthur Causeway | ||
| Miami Beach | Also 5th Street (east/west), then Collins Avenue (north/south) | |||
| Also Collins Avenue (northbound) and Indian Creek Drive (southbound from SR 112 to 26th Street) | ||||
| Also Collins Avenue (northbound) and either Indian Creek Drive (southbound in 2 separate segments) or Collins Avenue | ||||
| Also Collins Avenue (northbound) and Abbott Avenue (southbound from SR 934 to Indian Creek Drive) and Indian Creek Drive (southbound from Abbott Avenue to SR 907) | ||||
| Surfside | Also Collins Avenue (northbound) and Harding Avenue (southbound from SR 922 to Abbott Avenue at SR 934) | |||
| Sunny Isles Beach | Also Collins Avenue from SR 826 to Bal Harbour, Bal Harbour Boulevard in Bal Harbour | |||
| Also Collins Avenue | ||||
| Broward | Hallandale Beach | Also South Ocean Drive from SR 858 to county line, Ocean Boulevard in Golden Beach | ||
| Hollywood | Also South Ocean Drive from SR 820 to SR 858 | |||
| Also North Ocean Drive from SR 822 to SR 820 | ||||
| Dania Beach | Also North Ocean Drive (north/south) and East Dania Beach Boulevard (east/west) | |||
| Fort Lauderdale | ||||
| Lauderdale-by-the-Sea | ||||
| Pompano Beach | ||||
| Deerfield Beach | ||||
| Palm Beach | Boca Raton | |||
| Delray Beach | ||||
| Boynton Beach | ||||
| Lake Worth | ||||
| Palm Beach | ||||
| West Palm Beach | ||||
| Riviera Beach | ||||
| North Palm Beach | ||||
| Martin | Stuart | |||
| Jensen Beach | ||||
| St. Lucie | Fort Pierce | |||
| Indian River | Vero Beach | |||
| Brevard | Indialantic | |||
| Melbourne | ||||
| Satellite Beach | ||||
| Cocoa Beach | ||||
| Cape Canaveral | ||||
| Indianola | ||||
| Cocoa | ||||
| Volusia | New Smyrna Beach | |||
| Port Orange | ||||
| Daytona Beach Shores | ||||
| Daytona Beach | ||||
| Ormond Beach | ||||