Why do you think president lincoln decided to support the construction of the transcontinental railroad, a very expensive project even though the civil war was still going on?

Unite the country-- Lincoln promised a transcontinental railroad during his campaign.

Lincoln believed the railroad was a way to unite the country which was his aim with the Civil War so it fell right in line with his plan for the war. The railroad would help supply western forts and settlements as well as bring resources from the west to the east more quickly. Most importantly it would connect the country creating a more united Union.