Viaducts are a type of bridge that spans deep trenches and canyons or urban roads, supported by tall towers or pillars. They are composed of columns and beams that cross obstacles such as rivers and roads and can be used for both urban transportation and transporting heavy goods.

The history of the viaduct dates back to the 19th century when it was mainly used for building railways and transporting coal.

In the early 20th century, with the advent of automobiles, viaducts began to be used in urban traffic. The world's first urban elevated highway was built in 1915 in Detroit, United States, and this new type of urban transportation quickly spread across the country. By the 1950s, the number of viaducts in the United States had reached a significant scale.

Viaducts can be divided into different types based on their structural forms, including suspension viaducts, steel box girder viaducts, and steel arch viaducts.

A suspension viaduct has one or more suspension cables as the main load-bearing components. Its characteristic is that the bridge deck suspended on the suspension cables does not come into contact with the piers, allowing for a larger span on the bridge deck. Suspension viaducts are often used to span wider rivers or bays.

A steel box girder viaduct is composed of a series of steel box girders. A steel box girder is a steel structure with a rectangular or trapezoidal cross-section, which has good rigidity and load-bearing capacity. Steel box girder viaduct decks can be assembled relatively quickly, making construction relatively fast.

A steel arch viaduct has a steel arch as the main bearing component. The shape of the steel arch can be a single curve, double curve, or trapezoid, and it is characterized by a vault that can be kept stable. Steel arch viaducts are often used to cross canyons, rivers, and other areas with complex terrain.

When designing urban rail transit viaducts, the impact on the landscape should be considered first. While considering the structural requirements and strength requirements of the structure itself, attention should be paid to the artistic shape of the bridge.

The beautification design of the structure should be placed in a prominent position so that the viaduct becomes a beautiful landscape of the city.

The design requirements of urban viaduct bridges are the same as those of general bridges, and attention must also be paid to selecting the minimum building height to reduce the length of the bridge and the length of the approach road.

The silhouette of the viaduct should be designed to be light and harmonious with the surrounding environment. The location of the piers and the type of foundation must match the layout of the urban underground pipelines to reduce the workload of demolition as much as possible.

In addition, the design of urban viaducts needs to consider the impact on the surrounding environment, such as noise and vibration.

Appropriate sound insulation and seismic isolation measures should be adopted during the design process to reduce disturbance to surrounding residents and buildings. Maintenance and management issues of viaducts need to be considered as well, including regular inspections, repairs, and updates.

With the acceleration of urbanization and the continuous development of transportation, urban viaducts will still play an important role in future development.

The design of future urban viaducts should not only consider the needs of transportation but also pay attention to the requirements of ecological environmental protection and sustainable development, creating a more intelligent and environmentally friendly urban transportation system.