Streamliner trains are a type of passenger train designed for speed and efficiency, characterized by their sleek, aerodynamic shapes. They became popular in the 1930s and 1940s, featuring smooth lines and often colorful designs. These trains were built to reduce air resistance, allowing them to travel faster than traditional trains. The introduction of streamliner trains revolutionized rail travel in the United States, with famous examples like the Union Pacific's City of Los Angeles and the Santa Fe's Super Chief. Their design not only improved performance but also enhanced passenger comfort, making train travel more appealing during the mid-20th century.