Over the past 60 years, public spending on infrastructure has generally tracked the growth of the U.S. economy. Total public spending on infrastructure as a share of gross domestic product (GDP), normalized in 2014 dollars, has been relatively stable since 1956. Whether spending levels are adequate depends on the specifics.
Between 1964 and 1980, total public spending on highways decreased as a percentage of GDP and has been relatively flat since then. Spending on mass transit, rail, water resources, and water utilities as a percentage of GDP increased or remained relatively flat between 1980 and 2014.
Federal capital spending on highways has been declining for decades since the building of the Interstate Highway System in the 1950s and 1960s, even as total vehicle-miles traveled has been increasing. For both transportation and water infrastructure, total public spending and spending per capita generally rose until the 2008 financial crisis, and there is ample evidence that spending has picked up again in many places.