The National Highway System Designation Act of 1995 is prohibiting the national use of the metric system on roads across the United States. According to Wikipedia, the Act “designated about 259,032 km (160,955 miles) of roads, including the Interstate Highway System, as the NHS, restoring $5.4 billion in funding to state highway departments, giving Congress the power to prioritize highway system projects, repealing all federal speed limit controls, and prohibits the federal government from requiring states to use federal-aid highway funds to convert existing signs or purchase new signs with metric units.” (It is currently up the the states’ own decision to put metric signage). To speed up metrication efforts in the USA, the no-metric part of the NHSDA of 1995 has to be repealed to let metric signage be used nationally in the USA.