dramatically and that most development will be done along the current spatial template; (2) to show that the road system is carrying an increasingly heavy load, thus increasing congestion; and (3) to show that increased maintenance is required because of the aging road system. As we point out later, maintenance provides opportunities for mitigating or reducing the adverse ecological effects of roads, and such opportunities should be taken advantage of.

A large and extensive road system was already in place in the United States when cars became a major mode of transportation in the early twentieth century. The pattern of the system mirrored land uses and transportation corridors of the nineteenth century. Roads were narrow, primarily composed of dirt and gravel, and for the most part, followed existing topography. Before 1900, only 4% of the roads were paved, leading to poor and unreliable traveling conditions. Yet this system formed the template for the current system. Indeed, the road system has less than doubled in length since 1900, but the capacity has multiplied to accommodate an ever-increasing demand (Forman et al. 2003).

The development of the road system occurred in distinct eras, paced in part by technological transportation developments and resource availability. Each era marked a distinct change in a suite of variables (public values, policy, and fiscal resources) that influence road development.

The historical context for roads is an important consideration because history affects the current ecological effects of roads. For example, the designers of a modern interstate highway would be more likely to be sensitive to the hydrological and ecological effects of the project than the designers of a two-lane rural road built with county funds or 50 years ago without federal review. In addition, ecological impacts, environmental mitigation, and simple scale of the road surface area vary widely by road type. For example, depending on the scale of concern, an eight-lane interstate highway connecting major cities would have much greater fragmenting effects than a two-lane rural road.

Early Roads and Turnpikes

Early colonial routes were mostly natural surfaces intended to allow for the passage of wagons. These roads were built mainly to complement an extensive waterway transportation system. Roads provided local access and allowed the movement of people and goods where canals or

The National Academies of Sciences, Engineering, and Medicine
500 Fifth St. N.W. | Washington, D.C. 20001

Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement