BMW E46

The E46 experienced enormous success in all markets was widely considered the performance benchmark of its class. The longest spans usually require suspension bridges. The BMW E90 coupe will be released in 2006. For medium spans, trusses or box beams are usually most economical, while in some cases, the appearance of the bridge may be more important than its cost efficiency. In late 2005, BMW introduced the BMW E90 sedan which will replace the BMW E46 sedan. Bridges employing only compression are relatively inefficient structurally, but may be highly cost efficient where suitable materials are available near the site. The E46 automobile platform is the basis for the 1999 through 2005 BMW 3 Series. For a given site, kind of bridge employed and the materials used determine the total cost, a lifetime cost composed of materials, labor, machinery, engineering, cost of money, maintenance, refurbishment, risk potential, and ultimately, demolition and associated disposal, recycling, and reuse.

A bridge's economic efficiency will be site and traffic dependent, the ratio of savings by having a bridge (instead of, for example, a ferry, or a longer road route) compared to its cost. A more refined measure for this exercise is to weigh the completed bridge rather than measure against a fixed quantity of materials provided, a test that emphasizes economy of materials and efficient glue joints. The bridge taking the greatest load is by this test the most structurally efficient. In one common challenge young students are to be divided into groups of two or three and then to be given a fixed quantity of wood sticks, a specific distance to span, and a given glue, and then to construct a bridge that will be tested to destruction by the progressive addition of load at the center of the span.

A bridge's structural efficiency may be considered to be the ratio of load carried to bridge weight, given a specific set of material types. Bridges can also be classified by their lineage, which is shown as the vertical axis on the diagram to the right. In other cases the forces may be distributed among a large number of members, as in a truss, or not clearly discernible to a casual observer as in a box beam. The separation of forces may be quite clear, as in a suspension or cable-stayed span; the elements in tension are distinct in shape and placement.

Most bridges will employ all of the principle forces to some degree, but only a few will predominate. Bridges may be classified by how the four forces of tension, compression, bending and shear are distributed through their structure. The central bridge was reserved exclusively for the use of the Emperor, Empress, and their attendants. A set of five bridges cross a sinuous waterway in an important courtyard of the Forbidden City in Beijing, China.

Often in palaces a bridge will be built over an artificial waterway as symbolic of a passage to an important place or state of mind. Other garden bridges may cross only a dry bed of stream washed pebbles, intended only to convey an impression of a stream. This type, often found in east-asian style gardens, is called a Moon bridge, evoking a rising full moon. To create a beautiful image, some bridges are built much taller than necessary.

An aqueduct is a bridge that carries water, resembling a viaduct. For example, it may be a bridge carrying a highway and forbidden for pedestrians and bicycles, or a pedestrian bridge, possibly also for bicycles. In some cases there may be restrictions in use. A bridge is usually designed for trains, pedestrian or road traffic, a pipeline or waterway for water transport or barge traffic.

There are four main types of bridges: beam bridges, cantilever bridges, arch bridges and suspension bridges. The Oxford English Dictionary traces the origin of the word bridge to an Old Norse word bryggja, meaning "landing stage, gangway, or movable pier". With the advent of steel, which has a high tensile strength, much larger bridges were built, many using the ideas of Gustave Eiffel. With the rise of the Industrial Revolution in the 19th century, truss systems of wrought iron were developed for larger bridges, but iron did not have the tensile strength to support large loads.

The first engineering book on building bridges was written by Hubert Gautier in 1716. During the 18th century there were many innovations in the design of timber bridges by Hans Ulrich, Johannes Grubenmann, and others. Rope bridges, a simple type of suspension bridge, were used by the Inca civilization in the Andes mountains of South America, just prior to European colonization in the 1500s. Brick and mortar bridges were built after the Roman era, as the technology for cement was lost then later rediscovered.

The Romans also had cement, which reduced the variation of strength found in natural stone. The arch was first used by the Roman Empire for bridges and aqueducts, some of which still stand today. The first bridges were spans made of wooden logs or planks and eventually stones, using a simple support and crossbeam arrangement. .

The purpose of a bridge is to allow easier passage by providing a continuous more uniform more easily navigable route via what would otherwise be an uneven or impossible path for the particular kind of thing travelling or being transported, whether people, vehicles, trains, ships, liquids or whatever else. Designs may be built higher than otherwise needed in order to allow other traffic (particularly ship traffic) beneath. A bridge is a structure built to span a gorge, valley, road, railroad track, river, body of water, or any other physical obstacle. Pearl Harbor Memorial Bridge - USA, will be the first extradosed cable-stayed bridge constructed in the United States.

Zakim Bunker Hill Bridge - USA, built during Boston's Big Dig, the widest cable-stayed bridge. Victoria Falls Bridge - linking Zimbabwe to Zambia, built in 1905 as part of the projected Cape-Cairo railway. Vasco da Gama Bridge - Portugal, the longest bridge in Europe at 17.2 km. Trajan's bridge - Romania, ancient Roman bridge over the river Danube, only fragments visible.

Tyne Bridge - England, one of Northern England's most iconic structures. Tsing Ma Bridge - Hong Kong, the world's longest rail & road suspension bridge. Tower Bridge - London, England, and a symbol of this city. Tatara Bridge - Japan, largest span cable-stayed bridge.

Tacoma Narrows Bridge - USA, famous for its collapse due to aerodynamic effects. Sydney Harbour Bridge - Australia, arguably the best-known suspended-deck compression arch bridge. Sundial Bridge - USA, a dramatic single cantilever spar cable stayed span for pedestrians. San Francisco-Oakland Bay Bridge - USA, especially for seismic retrofit and eastern span replacement.

Québec Bridge - Canada, largest cantilever bridge in the world. Penang Bridge - Malaysia, longest bridge in Southeast Asia. Palace Bridge - St Petersburg, Russia, one of iconic images of the city. Overtoun Bridge, - Scotland, dogs have leaped to their deaths from this bridge, leading to urban legends.

Øresundbroen/Öresundsbron. Millau Viaduct - France, tallest bridge in the world. Menai Suspension Bridge - Wales, first road suspension bridge in the world. Mahatma Gandhi Setu - India, the longest river bridge in the world.

Mackinac Bridge - USA, Opened to traffic in 1957, connecting the two peninsulas of Michigan; held the title of the world's longest two tower suspension bridge between anchorages until the 1990s. Lupu Bridge- China, longest single steel arch. Lake Pontchartrain Causeway - USA, spanning Lake Pontchartrain in south Louisiana, it is the longest bridge in the world at 23.87 miles (38.41 km). Jamuna Bridge- Bangladesh, longest rail-road bridge in south asia , 2nd longest in world.

Confederation Bridge - Canada, world's longest bridge over waters that freeze. The Iron Bridge - England, the world's first iron bridge. Golden Gate Bridge - USA, arguably the most beautiful of its type. Forth Railway Bridge - Scotland, one of the most famous cantilever bridges in the world.

Akashi-Kaikyo Bridge - Japan, with the longest section span of 1.9 km.