1955 Louisiana Highway Renumbering - Post-1955 Numbering Practices

Post-1955 Numbering Practices

3xxx designations were given to all new post-1955 SRs, and were the only new type designations, until a few years ago when (in addition to 3xxx numbers) 12xx designations began to be assigned to new routes, starting with 1242 and working up (1241 is the highest-designated 1955 route). State routes in any range can and have been removed from the system, and there are many corresponding gaps in the numerical sequence. Numbers of deleted routes are not recycled into new routes as they are in other states; generally a new 32xx or 12xx number is assigned when a new number is needed. Many newer route designations are given to roads long having been on the state rolls, but which have been severed or isolated from its former designation by newer construction. Despite the high numbers, some roadways in the 3XXX series are major, heavily trafficked thoroughfares; an example is LA 3132, a connector between I-20 and I-49 in Shreveport—and a rare example, in Louisiana, of a state highway built in the multilane, divided, access-fully-controlled format typical of interstate highways.

Official US highway-state highway number duplications have been disallowed since 1955, but interstate-state highway duplications are permitted, and all interstate routes except 210 and 220 are duplicated in the rolls of state highway numbers. Most state highways with the same numbers as interstates are a comfortable distance away, with two exceptions: LA 59 and I-59, which exist within 20 miles (32 km) of each other in St. Tammany Parish, and which both intersect I-12; and LA 10 and I-10, which both flow east—west across south Louisiana. The confusion between LA 59 and I-59 became so substantial on the eastbound concourse of I-12 that Louisiana Department of Transportation and Development has posted "TO I-59" signs at the bottom of the eastbound exit ramp from I-12 at LA 59 to redirect, back to I-12 eastbound, motorists who confuse LA 59 as I-59.