Pre-1955 route numbering In the
original Louisiana Highway system in use between 1921 and 1955, the majority of LA 47 was designated as
State Route 61. It was created in 1921 by an act of the state legislature as one of the original 98 state highway routes. The southernmost portion of the route followed the existing Paris Road, originally platted in the early 19th Century as the main street of
Versailles, an ambitious town plan that evolved into the present community of Chalmette. North of town, Route 61 was projected to traverse the swamps until reaching the natural ridge along Bayou Sauvage that supported the roadbed of the
Old Spanish Trail, designated as
Route 2. Now known as Old Gentilly Road, this highway became the original alignment of US 90 upon its designation in 1926. Route 61 was constructed through the swamps north of Chalmette around the end of the 1920s. The route originally contained a
swing bridge across Bayou Bienvenue on the St. Bernard–Orleans parish line, the remains of which can still be seen immediately to the west of the present fixed span. In 1936, the entire length of Route 61 was improved from a gravel road to a paved road. Shortly afterward, a gravel extension was completed north to Hayne Boulevard, giving St. Bernard Parish residents direct access to Little Woods, an area on Lake Pontchartrain lined with recreational camps built over the water. This road did not become part of the state highway system at this time. However, in 1942, the Route 61 designation was extended slightly to connect with the newly constructed relocation of US 90 known as Chef Menteur Highway. Around the middle of the decade, the Gulf Intracoastal Waterway was dug through the area, necessitating a second bridge crossing on Route 61.
Post-1955 route history LA 47 was created in 1955 as a direct renumbering of former Route 61. With the 1955 renumbering, the state highway department initially categorized all routes into three classes: "A" (primary), "B" (secondary), and "C" (farm-to-market). This system has since been updated and replaced by a more specific
functional classification system. Since the renumbering, LA 47 has been extensively improved and reconstructed. Construction began in the early 1960s on I-10 running parallel to US 90 through New Orleans East. LA 47 was again extended north along Paris Road about to a planned connection with the future interstate highway. The resulting interchange was partially opened in April 1967 when I-10 was completed eastward from Paris Road to the
Twin Span Bridge across Lake Pontchartrain. That same year, a new high-level fixed span bridge on LA 47 across the Gulf Intracoastal Waterway was opened to traffic. Designed by the
Army Corps of Engineers, the
cantilever truss bridge with tied arch-suspended span contained four vehicular lanes and allowed all marine traffic to pass underneath unimpeded. Officially called the Paris Road Bridge, its original green painted surface led to its being called the "Green Bridge" by St. Bernard Parish residents. The I-10/LA 47 interchange was fully opened to traffic in October 1972 when the interstate was completed westward to Morrison Road near the
Industrial Canal bridge.
Interstate 510 By the early 1970s, a project was underway to reconstruct LA 47 as a modern four-lane highway connecting Chalmette with the new Gulf Intracoastal Waterway bridge. This involved the construction of a new roadway embankment through the swamp running parallel to the existing two-lane highway as well as a new fixed span bridge across Bayou Bienvenue. The entire corridor was intended to become part of
I-410, a planned southern loop around New Orleans designated in 1969 that would connect with I-10 on either side of the city. Construction was not completed until around 1980, three years after the I-410 loop was cancelled. However, the portion north of the Gulf Intracoastal Waterway bridge was retained as I-510, a short spur of I-10. The portion of LA 47 designated as I-510 was improved as an interstate-grade freeway beginning in 1985. While it required only of construction, the project was many years behind schedule mainly due to environmental-related concerns. A four-lane detour was paved on the west side of the right-of-way to serve through traffic during construction and is still in use today as a frontage road. The completed interstate spur was officially dedicated and opened to traffic by Louisiana Governor
Edwin Edwards on November 13, 1992 after seven years of construction and an expenditure of $82 million. It included new interchanges at Almonaster Boulevard (connecting to Old Gentilly Road), US 90 (Chef Menteur Highway), and Lake Forest Boulevard. Additionally, the US 90 interchange served as a grade separation for the parallel
Canadian National Railway (CN) line. The reconstructed route facilitated the movement of traffic between Chalmette and New Orleans East and provided a vastly improved outlet for St. Bernard and Plaquemines Parish residents during hurricane evacuations. ==Future==