Interstate 99 is an Interstate Highway in the United States with two segments: one located in central Pennsylvania, and the other in southern New York. The southern terminus of the route is near exit 146 of the Pennsylvania Turnpike (I-70 and I-76) north of Bedford and the northern terminus of the Pennsylvania segment is near exit 161 of I-80 near Bellefonte. The New York segment follows US 15 from the Pennsylvania–New York border to an interchange with I-86 in Corning.
Unlike most Interstate Highway numbers, which were assigned by the American Association of State Highway and Transportation Officials (AASHTO) to fit into a grid, I-99’s number was written into Section 332 of the National Highway System Designation Act of 1995. I-99 violates the AASHTO numbering convention associated with Interstate Highways, as it should lie to the east of I-97 but instead lies east of I-79 and west of I-81.