Interstate 12 is a 85.59 m long Interstate Highway in Louisiana , connecting Interstate 10 at each end . Interstate 12 ( I-12 ) is an intrastate Interstate Highway located entirely within the state of Louisiana . I-12 starts in Baton Rouge at Interstate 10 , and travels along the North Shore of Lake Pontchartrain before ending at the intersection of Interstate 10 and Interstate 59 near Slidell .