Two column bent viaduct; traveler for erecting forms, central park tunnel - (in this tunnel ducts are built in the sidewalls).

The history of the subway, or underground railway, dates back to the 19th century. The first underground railway was the Metropolitan Railway in London, which opened in 1863. It was proposed for London by Charles Pearson, a city solicitor, as part of a city-improvement plan shortly after the opening of the Thames Tunnel in 1843. The subway quickly became a popular mode of transportation in urban areas, as it allowed people to travel quickly and efficiently through the city. Over time, many cities around the world built their own subway systems, and today, subway trains are a common sight in many major cities. The technology used in subway systems has evolved over time, and modern trains are faster and more efficient than ever before.