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 Commodore Point Expressway, but more commonly referred to by locals 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 is the longest river in the U.S. state of Florida and its most significant for commercial and recreational use. At long, it winds through or borders twelve counties, three of which are the state's largest. The drop in elevation from the headwaters to the mouth is less than ; like most Florida waterways, the St. Johns has a very slow flow rate at a third of a mile an hour (0.2 km/h), and is often described as "lazy".Whitney, p. 215. It is one of a small number of rivers in the United States to run north. Numerous lakes are formed by the river or flow into it, but as a river its widest point is across, spanning several miles between Palatka and Jacksonville, the latter being the largest urban area on the river. The narrowest point is in the headwaters, an unnavigable marsh in Indian River County. In all, 3.5 million people live within the various watersheds that feed into the St. Johns River.Belleville, p. xxi.

Comprising a drainage basin of , the St. Johns is one of the major interior wetlands of Florida.The St. Johns River: Nominated as an American Heritage River, Environmental Protection Agency. Retrieved on July 17, 2009.Whitney, p. 136. It is separated into three major basins and two associated watersheds for Lake George and the Ocklawaha River, all managed by the St. Johns River Water Management District. Like all waterways in Florida, the St. Johns is fed primarily by rainfall, most of which is immediately deposited into the river and its tributaries as stormwater runoff. Much of the water flowing into the St. Johns also comes from the Floridan Aquifer, a natural underground reservoir that serves as the fresh water source for populations living north of St. Petersburg. The St. Johns itself is being considered as a potential fresh water source for 2020 as populations continue to grow, taxing the Floridan Aquifer.

A vast variety of people have lived on or near the St. Johns, including Archaic people, Timucuan, French and Spanish settlers, Seminoles, slaves and freemen, Florida crackers, land developers, tourists, and retirees. It has been the subject of William Bartram's journals, Marjorie Kinnan Rawlings' books, and Harriet Beecher Stowe's letters home. Although Florida was the location of the first permanent European colony in what would become the United States, it was the last U.S. territory on the east coast to be developed, and it remained a wilderness frontier into the 20th century. When attention was turned to the state, however, much of the land was rapidly overdeveloped in a national zeal for progress. The St. Johns, like many Florida rivers, was altered to make way for agricultural and residential centers and suffered severe pollution and human interference that has diminished the natural order of life in and around the river. It was named one of 14 American Heritage Rivers in 1998 but was included on a list of America's Ten Most Endangered Rivers in 2008.Ball, David (April 14, 2008).St. Johns River Makes ?Endangered' List, Jacksonville Financial and Daily Record. Retrieved on July 17, 2009. Restoration efforts are underway for the basins around the St. Johns as Florida continues to deal with population increases in the river's vicinity.