High Quality Content by WIKIPEDIA articles! 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. I-12 is only 85 miles long between Baton Rouge and Slidell, while I-10 takes 108 miles to travel between the same two points, so I-12 is heavily-used as a shortcut for through traffic on I-10. I-12 is six lanes from its western terminus until Exit 12 (Juban Road) at which point it becomes a four-lane highway to its eastern terminus.