Interstate 12

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.

In 1993, the state legislature renamed Interstate 12 as the Republic of West Florida Parkway. In 2003, signs identifying the highway's official name and bearing the flag of the Republic of West Florida were erected by the Louisiana Department of Transportation and Development in order to highlight the unique history of Louisiana's Florida Parishes.

The highway is relatively short for a mainline route at only 85 miles (137 km). While Interstates 19, 66, 97, and the partially completed Interstate 99 are all shorter, none of these has two termini with the same route, much less within the same state (I-99 will eventually extend into New York). Compare the length of I-12 to that of the 73.5-mile (118.3 km) I-295 in New Jersey and Delaware, or the 72.8-mile (117.2 km) I-405 in California, or even the 132-mile (212 km) I-476 in Pennsylvania, all of which are auxiliary Interstate Highways.