Economists at the Federal Reserve Bank of San Francisco studied the effects of unexpected grants to states for Federal-Aid Highways affected gross state product (GSP, or the gross domestic product (GDP) of a state). They found that an unexpected $1 increase in federal highway grants to a state resulted in a $2 increase in GSP. The economic effect was double the amount of the grant. In the short term, effects on GSP were even greater.
You can read the unpublished paper here→ or read a summary here→. Additional posts and articles related to the impact of infrastructure investment include: