Christopher T. Baer first joined the Hagley Museum and Library in August 1977 as a student in the Hagley Fellowship Program. From 1978 to 1981 he was the principal researcher and cartographer in a project to map transportation in the antebellum Mid-Atlantic States as part of Hagley's Regional Economic History Research Center. The first volume, "Canals and Railroads of the Mid-Atlantic States, 1800-1860," was published in 1981, at which point the funds were exhausted and the Center subsequently dissolved.

Because many of the same primary resources were involved, data was also collected for a projected companion map series on antebellum roads and turnpikes and entered in the project's data base of file cards and sketches. Following the publication of the canal and railroad study and the disbanding of the project team, Baer decided to collate and plot this data as a personal research project, supplementing the project files with additional research. The result was a very tentative time series of maps at the same 1:1,000,000 scale as the railroad maps, taken at the same 15-year intervals between 1815 and 1860.

While 19th century toll roads had been studied at a very high level of generality (by Durrenberger in 1931), or at the state or county level for selected states and counties, there has been no analysis of the entire network of a multi-state economic region other than New England. These initial maps, though tentative, were adequate to show two distinct toll road regimes. The first embraced New England, upstate New York, northern New Jersey and northeastern Pennsylvania and was all but coterminous with Yankee migrations and the New England culture zone. It was characterized by rapid and cheap turnpike construction in the early years of the century, including what was probably overbuilding from an economic standpoint, followed by shake-outs and abandonments after about 1830. The area to the south, including southern New Jersey, the rest of Pennsylvania and down through Virginia and present West Virginia, that is areas without a dominant presence of New Englanders, built more slowly and substantially, continuing to build dense radial webs around major cities and market towns, especially in prime agricultural areas, even after the Civil War, and with many more toll roads surviving to be condemned by state highway departments for public paved roads in the 1910s and 1920s. A brief 1845-1860 craze for plank roads, which greatly reduced rolling friction but rotted faster than they could earn their replacement costs, was most pronounced in New York State where older turnpikes had been abandoned already, but could be found to a lesser degree in each of the other states.

Unfortunately, unlike railroads and canals, authoritative documentation for toll roads was highly decentralized, making a research project to produce an accurate regional map too expensive to be practical. State laws and local histories contained some clues, and in antebellum Virginia, the Board of Public Works provided centralized engineering services and collected regular annual reports and maps. However, the documents needed to fix the life span of a 19th century turnpike are the license to take tolls issued by the governor and the deeds surrendering the road to the township, county or state. The former for Pennsylvania, in the governors' desk diaries, have been published only to about 1835 and appear lacking for the other states north of the Potomac. Collecting definitive abandonment dates would involve checking the deed records of hundreds of counties over a wide geographic region. Thus the project did not proceed beyond the 1:100,000 maps and a series of larger scaled compilation sheets for parts of the region.

After the project lay fallow for several years, Baer was approached by Daniel Klein, an economist, and John Majewski, then a doctoral candidate in economic history, who were investigating the economic aspects of toll roads, especially the free-rider problem, mostly using New York State as a test case. Baer acted as geographer and cartographer. Klein had located a register of all plank roads at Albany, which when combined with contemporary maps and other accounts made it possible to construct a plank road map of the state of reasonable accuracy, and from it measure mileages at five-year intervals. Mileage by county could then be compared with other economic and population statistics. The turnpike study was more problematical, given the constraints listed above, but resulted in an improved map for 1830. Two journal articles were published, with maps and figures by Baer and economic analysis and text by Klein and Majewski.