The Plan of Chicago’s scheme for diagonal thoroughfares extended to the edge of the city, although most of the construction of new arteries was supposed to occur in the city center. In one sense the scheme revitalized pathways that long preceded the arrival of newcomers from Europe and Africa. The site of Chicago had long been an important hub of trade and communication for Native Americans, who had developed an extensive system of trails that linked the country to the north, west, and south to the region and its many portages. Most of the radial routes proposed by the Plan extending to the city limits were existing highways, ultimately based on these Indian routes. Burnham and Bennett valued these routes, but argued that an exclusively radial pattern of these highways that converged on the city center was a major cause of congestion. By laying out a lattice of new intersecting diagonals, they hoped to redirect and diminish this congestion in the center and distribute it throughout the city. Diagonal thoroughfares were particularly important to their vision of city streets because they saw the primary existing grid of streets, based on the division of land dictated by the U.S. Public Land Survey, as inflexible and restrictive. “[W]hen the city increases in the population… diagonals become necessary in order to save considerable amounts of time and to prevent congestion by dividing and segregating the traffic.” (p. 89) The grid lain out in conformity with the U.S. Public Land Survey was suitable for land division, perhaps, but not for the efficient movement of traffic across town. However, it would be difficult to override the grid with new streets because the shape of private land holdings had been determined by the grid. This is why the pre-existing radials, which mostly preceded the establishment of the grid, were of such enduring importance, while most of the proposed intersecting diagonals never came to pass.
White, Richard. The Middle Ground: Indians, Empires, and Republics in the Great Lakes Region, 1650-1815. Cambridge and New York: Cambridge University Press, 1991.
Quaife, Milo M. Chicago’s Highways Old and New: From Indian Trails to Motor Road. Chicago: D.F. Keller & Company, 1923.
“Chicago. Existing and (in Red) Proposed Diagonal Arteries,” from Plan of Chicago (Chicago: The Commercial Club, 1909), pl. XCI. Chicago History Museum, ICHi-68615