Hart Bridge -- Traffic count average daily: 47,000

The Isaiah David Hart Bridge is a cantilever bridge that spans the St. Johns River in Jacksonville, Florida. It is named after Isaiah Hart, the founder of Jacksonville. The bridge has traditionally been painted green and is often referred to as "The Green Monster" by locals.Florida Times UnionJax Air News The westbound end of the bridge delivers drivers to downtown Jacksonville or Martin Luther King Expressway, while the eastbound end sends motorists to Beach Boulevard. Daily traffic is 47,000 vehicles. The stretch of highway between downtown and Beach Blvd. is known as the Hart Bridge Expressway.

Isaiah David Hart (November 6, 1792 ? 1861) was an American plantation owner and the founder of Jacksonville, Florida. Originally from Georgia, he began setting out the plans for the town in 1822 after moving to the area named Cowford. The Isaiah D. Hart Bridge over the St. Johns River in Jacksonville is named after him.

His son, Ossian B. Hart, became the tenth governor of Florida in 1873.

A cantilever bridge is a bridge built using cantilevers, structures that project horizontally into space, supported on only one end. For small footbridges, the cantilevers may be simple beams; however, large cantilever bridges designed to handle road or rail traffic use trusses built from structural steel, or box girders built from prestressed concrete. The steel truss cantilever bridge was a major engineering breakthrough when first put into practice, as it can span distances of over , and can be more easily constructed at difficult crossings by virtue of using little or no falsework.

The St. Johns River (officially Saint Johns River, but commonly spelled 'St. Johns River') is the longest river in the U.S. state of Florida, stretching 310 miles (500 km) from Indian River County to the Atlantic Ocean in Jacksonville in Duval County. The Saint Johns is north-flowing, which is somewhat unusual among U.S. rivers

The elevation change from headwaters to mouth is only about 30 feet, making the St. Johns one of the worlds "laziest" rivers. Extremely low velocity and low volume of flow, combined with the generally level elevation, cause the St. Johns to spread out to a great width for much of its course. During periods of low flow, the river can be influenced by tides as far south as Lake Monroe - 161 miles inland. For a distance of over twenty miles before arriving at downtown Jacksonville, the river's average width exceeds two miles and some points exceed three miles in width. The slow flow of the St. Johns makes it difficult for pollutants to be flushed from the waters, which has become a serious problem for the river ecosystem. It was designated as one of the American Heritage Rivers in 1997 and pegged by an environmental organization as the 6th Most Endangered River in America in 2008.http://www.ens-newswire.com/ens/apr2008/2008-04-17-01.asp Still, the river is home to numerous species of plants and animals. It is not uncommon to see dolphins in the river east of Jacksonville and manatees in the springtime when the water warms up. Alligators, bald eagles, ospreys, stingrays, and many species of fish?both salt and fresh water?are found living in the river and on its banks. The entire basin is managed by the St. Johns Water Management District.