In the first quarter of the 20th century, as the automobile gained in popularity, a system of roads began to develop informally through the actions of private interests, these were known as auto trails. They existed without the support or coordination of the federal government, although in some states, the state governments participated in their planning and development. The first of these National Auto Trails was the Lincoln Highway, which was first announced as a project in 1912.
With the need for new roads being so significant, dozens of new auto trails were begun in the decade following. One such roadway was the Jefferson Davis Memorial Highway, which was sponsored by the United Daughters of the Confederacy. The UDC planned the formation of the Jefferson Davis as a road that would start in Washington, D.C. and travel through the southern states until its terminus at San Diego. More than ten years after the construction of the Jefferson Davis was begun, it was announced that it would be extended north out of San Diego and go the Canadian border.
In the mid-1920s, the disparate system of national auto trails had grown cumbersome, and the federal government imposed a numbering system on the nations's highways. Using a system of even numbers for east–west routes and odd numbers for north–south routes, the numbers were imposed on the auto trails. And rather than designate one number for each auto trail, different sections of each trail were given different numerical designations. However the UDC petitioned the U.S. Bureau of Public Roads to designate the Jefferson Davis as a national highway with a single number. The Bureau's reply casts doubt on whether or not the JDMH ever really existed as a transcontinental highway:
A careful search has been made in our extensive map file in the Bureau of Public Roads and three maps showing the Jefferson Davis highways have been located, but the routes on these maps are themselves different and neither route is approximately that described by you, so that I am somewhat at a loss as to just what route your constituents are interested in. For instance, there is the Jefferson Davis Memorial Highway which extends from Miami, Florida to Los Angeles (but not to San Francisco); and there is another Jefferson Davis Highway shown on the Rand-McNally maps which extends from Fairview, Kentucky the site of the Jefferson Davis monument, by a very circuitous route to New Orleans, but I find no route whatever bearing the name Jefferson Davis extending from Washington, D.C. to San Francisco. (emphasis added)
This problem may well have been the fault of the UDC themselves. In addition to the planned transcontinental route, they also designated an auxiliary route running from Kentucky to Mississippi, as well as another that ran through Georgia. These ancillary routes were intended to commemorate important venues in Davis' life, but they also contributed to the confusion of the federal government in trying to locate exactly where the Jefferson Davis highway traveled. What is known is that when numbered highways came into existence, the Jefferson Davis National Highway was split among U.S. 1, U.S. 15, U.S. 29, U.S. 61, U.S. 80, U.S. 90, U.S. 99, U.S. 190 and others. But today many of these numbered routes themselves are no longer extant, having been supplanted by the Interstate Highway System.
Remaining portions of the Jeff Davis
Although it may not be possible to view the entire length of the JDMH on a map today, many parts of it still exist, scattered across the country. Here is an incomplete listing of some of the places today where one can see pieces of the Jefferson Davis highway.
The original eastern terminus of the highway can still be found near the Virginia end of the 14th Street Bridge, which crosses the Potomac River from Washington, DC. The terminal marker was here until the 1960s, when it was moved to a nearby location for safety reasons.
The northeastern section of the highway approximates the route of the older Washington and Alexandria Turnpike, which received its charter from the United States Congress in 1808. A street in Crystal City once designated as "Old Jefferson Davis Highway" parallels the east side of U.S. Route 1, part of which is the present Jefferson Davis Highway in the area. This street, which was the original route of the highway, now ends before reaching the 14th Street Bridge. On September 20, 2011, the Arlington County Board (see Arlington County, Virginia#Government) voted to change the name of the street to "Long Bridge Drive" after the chairman of the Board, who was originally from the northeastern part of the United States, stated: "I have a problem with 'Jefferson Davis' ... There are aspects of our history I'm not particularly interested in celebrating".
The Jefferson Davis Highway traverses through the state for 170 miles (270 km). Starting at the North Carolina state line, it follows US 1 to the Georgia state line near Augusta. Several monuments can be found along the route including in Camden and Aiken.
Highway markers can still be seen in certain spots along the old main transcontinental route through the state of Georgia.
An auxiliary route through Georgia went south of the main route through Irwin County and Irwinville, where Davis was ultimately captured at the end of the Civil War. This route followed Georgia State Route 32 to the west of Irwinville, into neighboring Turner County, where today S.R. 32 retains the official name of "Jefferson Davis Highway".
In LaGrange, a monument exists at the northeast corner of LaGrange College, which is within 1 mile (1.6 km) of Confederate Senator Benjamin Hill's National Historical Home.
In Baton Rouge, the highway follows Government Street to the levee and then north along the levee to Florida Street (U.S. 190 Business Route). The road continued west across the Mississippi River on a now closed ferry into Port Allen, Louisiana.
In Port Allen, Jefferson Highway goes north to the northern end of the town. The highway then follows west along Louisiana Highway 986. The roadway later changes to Louisiana Highway 76 and follows that highway into the town of Rosedale, Louisiana. It continued up northward through the Town of Maringouin, Livonia Fordoche on Louisiana Highway 77. Then crossed the Atchafalaya River via ferry Louisiana Highway 10 in the City of Melville, Louisiana.
Markers for the highway indicate a main route from Orange to El Paso via Austin, with a "Coastal Route" spur branching at Houston and heading south to Brownsville. At least 20 markers are still in existence across the state. 
Parts along I-10. There is a marker at a rest stop that indicates the highway and that the marker was paid for by the Daughters of the Confederacy in 1955.
The western terminus of the highway is identified by a monument on Horton Plaza, in downtown San Diego. The formal opening of the highway at this terminus was performed by President Warren Harding. Photographs of this event are available in the archives of the San Diego Union-Tribune and in the files of the San Diego Historical Society.
In 1939, the Washington state legislature named Highway 99 as the "Jefferson Davis Highway", making it the final component of the Jefferson Davis Memorial Highway. In 2002, the state's House of Representatives unanimously approved a bill that would have removed Davis' name from the road. However, a committee of the state's Senate subsequently killed the proposal.
In 1998 a marker of the "Jefferson Davis Memorial Highway" in Vancouver, Washington was removed by city officials. It was subsequently moved twice, and eventually was placed alongside Interstate 5 on private land purchased for the purpose of giving the marker a permanent home.