What official act started the transcontinental Railroad?

The official act that started the transcontinental railroad was the Pacific Railway Act of 1862. This legislation authorized the construction of a railroad and telegraph line from the Missouri River to the Pacific Ocean, granting land and financial support to the Union Pacific and Central Pacific railroads. The act aimed to promote westward expansion and facilitate commerce and communication across the country. Construction began shortly after the act was signed into law by President Abraham Lincoln.