The significance of the Transcontinental Railroad in shaping America's infrastructure lies in its role in uniting the eastern and western parts of the country. Completed in 1869, it facilitated the movement of goods, resources, and people across vast distances, driving economic growth and expansion. The railroad also spurred settlement in the West, contributing to the Manifest Destiny ideology. Additionally, it fostered improvements in communication, led to the development of towns along its route, and ultimately reshaped not only transportation but also societal dynamics across the nation.