March 26 (Reuters) - Baltimore's Francis Scott Key Bridge collapsed on Tuesday after a container ship smashed into it, plunging cars into the water. It is a major traffic and transportation hub for the U.S. East Coast and the entry point to the Port of Baltimore.

BRIDGE HISTORY: The four-lane steel bridge opened in 1977 after five years of construction and spans 1.6 miles (2.6 km). It crosses the Patapsco River, where U.S. national anthem author Francis Scott Key wrote the "Star Spangled Banner" in 1814 after witnessing the British defeat at the Battle of Baltimore and the British bombing of Fort McHenry. It has 185 feet (56 meters) of vertical clearance.

Built at an estimated cost of $110 million, it allowed for more traffic lanes and carried lower operating and maintenance costs than a tunnel.

TRAFFIC AND TRANSPORT INFO: The bridge carries 11.3 million vehicles a year, the Maryland Transportation Authority says, on the I-695 highway that circles Baltimore, also known as the Baltimore Beltway.

GATEWAY TO BALTIMORE PORT: The bridge leads to the Port of Baltimore, the deepest harbor in Maryland's Chesapeake Bay. It is the busiest U.S. port for car shipments, handling more than 750,000 vehicles in 2023, according to official data. It is also the largest U.S. port by volume for handling farm and construction machinery, as well as agricultural products, and a cruise terminal, with operators Norwegian, Carnival and Royal Caribbean, all using the port for Caribbean, Canadian and other Atlantic destinations.

OTHER BRIDGES IMPACTED

Other structures along the route include a 0.64-mile dual-span drawbridge over Curtis Creek and two 0.74-mile parallel bridge structures that carry traffic over Bear Creek, near Bethlehem Steel's Sparrows Point plant.

COMMUTE DISRUPTIONS: Maryland's Transportation Authority called the incident a "major traffic alert" and redirected cars to the I-95 or I-895 highways. Large trucks are prohibited from using the 1-95 tunnel route that goes under the Baltimore harbor.

BALTIMORE PORT TRAFFIC: Because of the bridge's collapse, ships are not leaving the Port of Baltimore. More than 40 ships remained inside the port including small cargo ships, tugboats and pleasure craft, data from ship tracking and maritime analytics provider MarineTraffic showed. At least 30 other ships had signaled their destination was Baltimore port, the data showed.

(Reporting by Jyoti Narayan in Bengaluru and David Shephardson in Washington; Editing by Nick Macfie, Heather Timmons and Lisa Shumaker)