The National Rail Freight Infrastructure Capacity and Investment study provides is an assessment of the long-term capacity expansion needs of the continental U.S. freight railroads. It focuses on 52,340 miles of primary rail freight corridors, about one-third of all continental U.S. rail freight miles. The study estimates that meeting the U.S. Department of Transportation's projected 88 percent increase in demand for rail freight transportation in 2035 will require an investment in infrastructure of $148 billion (in 2007 dollars) over the next 28 years. Class I railroads' share is projected to be $135 billion, with $13 billion projected for short line and regional freight railroads. The study was commissioned by the AAR at the request of the National Surface Transportation Policy and Revenue Study Commission.