Toll fees are used for several things including maintenance, upgrading and replacement of existing roads as well as building new roads, according to the U.S. Department of Transportation. The specific use of toll funds is decided by state government and overseen by the Federal Highway Administration, which is part of the Department of Transportation.
It is a common misconception that American interstates are already paid for. The interstate system was initially funded under the Federal Aid Highway Act of 1956. This federal legislation, however, does not account for and fund all necessary maintenance and building as the nation ages and grows. As the interstate system ages, significant additional funds are required each year to keep the interstate system in safe operating order, according to the FHWA. Examples of the maintenance required include the filling of potholes, replacement of guard rails, dividing line repainting and tar maintenance. Additionally, to keep the highways functioning under the most current technology, regular funding is required for technological improvement.
There is a federal per-gallon gas tax, which was most recently raised in 1993. Since that time, the value of the tax has decreased significantly, which requires states to make up the difference in road maintenance funds through tolls and other means. Unfortunately, as of 2015 the Federal Highway Trust fund is nearly insolvent, and the problem is likely only to worsen as the costs of materials and labor increase with inflation, notes The International Bridge, Tunnel & Turnpike Association.