What the Overseas Highway is and where it goes
The Overseas Highway is U.S. Route 1 as it runs through the Florida Keys, a chain of islands stretching about 120 miles southwest from the mainland near Miami to Key West. The road itself is roughly 113 miles long and connects the Keys with a series of bridges, causeways, and fills. It is the only road in and out of the Keys — there is no alternate route, and no ferry service to the mainland.
The highway passes through or near most of the inhabited Keys, including Key Largo, Islamorada, Marathon, Big Pine Key, and Key West. The route number changes from U.S. 1 to the Overseas Highway designation only informally; official signs still read U.S. 1. The road is a National Scenic Byway, which means it has been recognized for its outstanding scenic, historic, recreational, cultural, archaeological, or natural qualities — in this case, primarily the water views and the unique ecosystem of the Keys themselves.
The highway was originally built between 1912 and 1938 as a railroad, the Overseas Railroad, which connected Key West to the mainland. A 1935 hurricane destroyed much of the railroad, and the roadbed was later converted to a highway. Parts of the original railroad bridges are still visible alongside or incorporated into the current road.
Key Takeaways
- The Overseas Highway is the only road connecting the Florida Keys to the mainland, making it essential infrastructure rather than optional scenery.
- The route spans roughly 113 miles and passes through or near Key Largo, Islamorada, Marathon, Big Pine Key, and Key West.
- The highway was built on the roadbed of the Overseas Railroad, which operated from 1912 until a 1935 hurricane destroyed it.
- Driving the full route typically takes three to four hours without stops, though most visitors stop multiple times to view the water and visit towns along the way.
The bridges and causeways that make up the route
The Overseas Highway is not a continuous road in the traditional sense. It is made up of bridges, causeways, and short road segments that connect the individual Keys. The most famous of these is the Seven Mile Bridge, which spans Pigeon Key and connects Marathon to Bahia Honda Key. The bridge is about 6.79 miles long and was completed in 1912 as part of the original railroad. The current road bridge was finished in 1982 and runs parallel to the original railroad bridge, which is now closed to vehicle traffic but open to pedestrians and cyclists.
Other notable bridges include the Long Key Viaduct, a long causeway north of Islamorada, and numerous smaller bridges throughout the route. Many of these structures offer views of the Atlantic Ocean on one side and the Gulf of Mexico on the other. The bridges and causeways are relatively narrow, and the road has no median. Speed limits are typically 45 to 55 miles per hour, though they drop to 25 or 35 in populated areas.
The road is subject to occasional closures due to hurricanes, storm surge, or damage. When a major hurricane threatens, the Keys may be evacuated and the highway closed. After storms, the road is inspected for damage before it reopens. In recent years, rising sea levels and saltwater intrusion have become ongoing concerns for the long-term maintenance of the route.
Towns and stops along the route
The Overseas Highway passes through or near several towns, each with its own character and history. Key Largo, at the northern end, is known for diving and snorkeling, particularly around the John Pennekamp Coral Reef State Park. Islamorada, a village made up of several small islands, is a popular fishing destination. Marathon, roughly in the middle of the Keys, is the largest town on the route and serves as a hub for services, fuel, and food.
Big Pine Key is home to the Key Deer, a small endangered species found nowhere else in the world. The Key Deer Refuge protects habitat for these animals, and visitors can sometimes see them along the roadside, particularly at dawn and dusk. Key West, at the southern end, is the largest city in the Keys and a major tourist destination known for its history, culture, and nightlife. Key West is also the southernmost point of the continental United States.
Between these main towns are smaller communities, parks, and natural areas. Bahia Honda State Park, accessible from the highway, has beaches and trails. The Dry Tortugas, a national park, is accessible by boat or seaplane from Key West. Most visitors stop multiple times along the route to view the water, eat, or explore specific attractions.
Driving conditions and what to expect
The Overseas Highway is a two-lane road for most of its length, with limited passing opportunities. Traffic can be heavy, especially during winter months and holiday periods. The road is relatively straight and flat, but the lack of shoulders and the narrow width mean that driving requires attention. Fuel and food are available in the towns along the route, but services are not continuous — it is wise to refuel in Marathon or earlier if heading to Key West, as gas stations are less frequent in the lower Keys.
The speed limit is 55 miles per hour on most of the highway, dropping to 45 in some areas and 25 to 35 in towns. Enforcement is active, and speeding tickets are common. The road is open year-round, but weather can affect driving conditions. Summer brings heat and afternoon thunderstorms. Hurricane season runs from June through November, and the road may close during major storms. Winter is the most popular time to visit, with mild weather and lower humidity.
Rental cars are widely available in Miami and Key West. The drive from Miami to Key West takes roughly three to four hours without stops, though most people spend a full day or longer exploring the Keys. There is no public transportation along the highway itself, though some towns have local bus service.
History of the Overseas Railroad and its conversion to a highway
The Overseas Railroad was built between 1912 and 1938 by Henry Flagler, a railroad magnate who wanted to extend his Florida East Coast Railway to Key West. The project was one of the most ambitious engineering undertakings of its time, requiring the construction of dozens of bridges and causeways across open water. The railroad operated for 23 years, carrying passengers and freight to and from Key West.
On September 2, 1935, a powerful hurricane struck the Keys and destroyed much of the railroad infrastructure. The storm surge and wind damage were so severe that the railroad was never rebuilt. The roadbed and some of the bridges were later acquired by the state of Florida and converted to a highway. The Overseas Highway officially opened in 1938, using much of the original railroad alignment and some of the original bridges.
The original railroad bridge, the Seven Mile Bridge, was replaced by a new road bridge in 1982. The old railroad bridge is now a historic landmark and is open to pedestrians and cyclists. Other sections of the original railroad grade and bridges are visible from the current highway or have been preserved as historical sites. The history of the railroad is documented in museums and visitor centers along the route, particularly in Key West and Marathon.
Environmental and infrastructure challenges
The Overseas Highway faces several long-term challenges related to climate and sea level. Rising sea levels and saltwater intrusion threaten the road's foundation and the freshwater aquifer that supplies the Keys. Storm surge during hurricanes can temporarily close the road or cause damage that takes weeks to repair. The narrow width of the road and the lack of alternate routes mean that any significant damage can isolate the Keys from the mainland.
The Keys are also home to sensitive ecosystems, including coral reefs, mangrove forests, and seagrass beds. The highway and its traffic have environmental impacts, though efforts have been made to minimize them through wildlife crossings, speed limits in sensitive areas, and regulations on boat traffic. The Key Deer and other endangered species are protected by law, and the road passes through or near several protected areas.
Maintenance of the highway is ongoing and expensive. The road is subject to corrosion from saltwater, damage from storms, and wear from heavy traffic. The state of Florida and the federal government share responsibility for maintaining the route. Long-term planning for the highway includes discussions about resilience to climate change, though no major reconstruction projects have been announced.
Frequently Asked Questions
How long does it take to drive the Overseas Highway from Miami to Key West?
The drive is roughly 113 miles and takes three to four hours of driving time without stops. Most visitors spend a full day or longer, stopping in towns like Islamorada and Marathon to eat, explore, or view the water. Traffic can add time, especially during winter and holiday periods.
Is the Overseas Highway always open?
The highway is open year-round under normal conditions, but it closes during major hurricanes or when damage requires repairs. Closures are typically announced in advance, and the road usually reopens within days to weeks after a storm. Check current conditions with the Florida Department of Transportation before traveling during hurricane season.
Where can I see the original Overseas Railroad bridge?
The original Seven Mile Bridge, built in 1912, runs parallel to the current road bridge between Marathon and Bahia Honda Key. It is now closed to vehicles but open to pedestrians and cyclists. The old bridge offers views of the water and is a popular spot for photos and walking.
What is there to do along the Overseas Highway?
Towns along the route offer dining, shopping, and accommodations. Specific attractions include John Pennekamp Coral Reef State Park near Key Largo, the Key Deer Refuge on Big Pine Key, Bahia Honda State Park, and various museums and historical sites. Key West has beaches, restaurants, bars, and cultural attractions. Many visitors stop to view the water and take photos from the bridges.
Is there public transportation on the Overseas Highway?
There is no bus or shuttle service running the length of the highway itself. Some towns have local bus service, and ride-sharing services operate in Key West and other larger towns. A rental car or personal vehicle is the primary way to travel the route.