**8. Conclusion and recommendations**

The definition of infrastructure includes wide variety of structures, each one with a specific purpose and its function serves the development of the society. All elements of the infrastructure are connected and any issue of an individual part will affect the entire system, slowing down the economic growth.

Transportation infrastructure has the purpose to connect two places using aerial, land and maritime methods, developing a wide variety of structures to comply with its objective. Bridges are part of land infrastructure and are used as link between two places with difficult access using single roads or highways. These types of structures have higher construction costs per mile if they are compared with single roads; therefore, there must be a complete plan to develop the project, which should include the number of lines required to meet traffic flow, vehicle load, site, geometric and budget requirements.

Large bridges exist since hundreds of year ago, where its use was restricted to aqueducts, carriages and road connectors for travelers, using as construction material stone and wood. The introduction of train and vehicles on the industry with the development of structural steel and Portland cement, modern bridges began, increasing load capacity and span length to cover.

There is no specific formula to choose the best option of bridges, due large amount of factors that depends on the structure, as geometry of the bridge, the experience of the construction companies, materials, loads to be carried out, labor available, budget and local site restrictions. A whole process that involves planning, design, construction and maintenance of the structure must be established.

The best economical option for a bridge is the combination of the efficient interaction of geometry and material, taking advantage of tension elements as the main structure. As we can see in **Table 2**, cable-stayed and suspension bridge are the best economical option for span lengths higher than 1800 ft. (550 m), due tension capacity of the steel cables. The span recommendations of **Tables 1** and **2** are a combination of efficient stress capacity due proposed geometry, in alignment of low deformations and material savings, making lower costs and improving budgets.

While planning, design and construction stages of the bridge are carefully studied to ensure its functionality; maintenance is given less importance thinking that the structure will have its useful life without any problems, when reality implies a degradation process, due its use and environmental factors. Maintenance plan is needed to avoid over costs during the life of the bridge.

Wear and fatigue degradation can be carefully studied and analyzed during the design procedure process, which will be present on all structures. However, corrosion degradation depends of the local site environment, mainly humidity and water contact, considered automatically as maintenance plan. Some cases, this
