U.S. Route 15 enters Pennsylvania from Maryland near Gettysburg and goes on to pass through the Harrisburg area, before paralleling the Susquehanna River concurrent with U.S. Route 11 to Sunbury. US 15 then navigates through Williamsport before pushing toward New York state as a freeway along part of the future I-99 corridor. US 15 has business routes in Gettysburg and Mansfield.