Key West Drive & Overseas Highway Travel Guide: Mile Markers & Seven Mile Bridge

Overseas Highway Engineering History: Henry Flagler's Railway to Modern US-1

The route connecting Key Largo to Key West represents one of the greatest civil engineering achievements in American transportation history. Originally conceived as Henry Flagler's Florida East Coast Railway Overseas Extension in 1912, the railway corridor was destroyed by the historic 1935 Labor Day Hurricane. Subsequently acquired by the state, the surviving viaducts, bridge piers, and coral causeways were converted into the modern two-lane Overseas Highway (US Route 1).

Modern motorists traverse 42 distinct bridge structures spanning emerald shallow flats, open Atlantic ocean passages, and tidal straits. The crowning centerpiece is the Seven Mile Bridge (35,862 feet), elevated 65 feet at its highest navigational apex to permit sailboat passage beneath. Concrete segmental box-girder spans engineered during the massive 1980s replacement project replaced the original railway roadbed, providing modern safety shoulders, storm-resistant pilings, and high-efficiency drainage.

Alongside the active automotive bridge, portions of the historic railway viaduct remain preserved as the Florida Keys Overseas Heritage Trail (FKOHT). Pedestrians, cyclists, and saltwater anglers can traverse the Old Seven Mile Bridge out to Pigeon Key, a historic 5-acre island at MM 44.8 that housed railway construction workers over a century ago. This continuous multi-use pathway connects mainland trail networks to the southernmost terminal marker in Key West.

Speed Enforcement Zones, Passing Corridors & Hurricane Evacuation Logistics

Unlike mainland interstate highways, US-1 through the Florida Keys operates as an undivided arterial roadway with intermittent passing lanes. Florida Highway Patrol (FHP) and the Monroe County Sheriff's Office maintain active radar patrols throughout the corridor.

During emergency evacuation operations prompted by hurricane watches, Monroe County Emergency Management executes a phased exodus model. Tourists and transient boaters are ordered to evacuate 48 to 72 hours prior to tropical storm force wind onset, followed by resident zones. When sustained bridge wind speeds surpass 40 mph, law enforcement locks down high-level spans including Seven Mile Bridge, Long Key Bridge, and Tavernier Creek, isolating island sectors until winds subside.

Fuel Optimization, Electric Vehicle Charging & Roadside Pullovers

Fuel stations and DC fast charging facilities are distributed along key island commercial centers in Key Largo (MM 100), Islamorada (MM 81), Marathon (MM 50), and Big Pine Key (MM 30). Drivers operating electric vehicles should note that highway headwinds over bridges can slightly reduce range estimates. Planning a 15-minute scenic rest stop at Bahia Honda State Park or the Seven Mile Bridge pedestrian walkway offers an ideal balance of charging and panoramic vistas.

Vehicle operators hauling boats or heavy trailers must also pay heed to brake temperature build-up when descending bridge approaches, particularly during stop-and-go weekend traffic. Utilizing lower transmission gearing rather than continuous friction braking preserves pad life and prevents trailer brake lock-up on wet road surfaces during sudden tropical squalls.

Key West arrival marks the culmination of the journey at US-1 Mile Marker 0 (intersection of Fleming and Whitehead Streets). Parking in historic Old Town is notoriously restricted; travelers are advised to park in designated municipal garages on Caroline Street or Simonton Street, utilizing the free Duval Loop transit trolley for downtown exploration.

Night driving across the Overseas Highway presents distinct navigational challenges requiring heightened motorist diligence. Vast stretches of causeway across Long Key, Channel 5, and Seven Mile Bridge feature zero roadside illumination, relying entirely on vehicle headlights and retroreflective road markers. Sudden saltwater spray kicked up by ocean trade winds can create micro-salt crusting on automotive windshields, reducing visibility unless drivers regularly activate windshield washers with fresh fluid.

Motorists departing mainland Florida during peak Friday afternoon rush hours can also evaluate the Card Sound Road (County Road 905A) arterial bypass. While the primary 18-Mile Stretch of US-1 delivers straight divided transit directly into North Key Largo, severe accidents can cause multi-hour gridlock. Card Sound Road routes vehicular traffic across a historic two-lane drawbridge spanning Card Sound into northern Monroe County, offering an indispensable secondary escape valve during holiday weekend congestion.