choices has grown in length and complexity. These questions extend from the most basic (e.g., should we consider transportation improvements?), to highly detailed consideration of the interactions between transportation improvements and other valued community features, to the final decision on whether action is warranted based on the projected benefits, costs, and impacts. Such decisions impact the livability of communities and require large bodies of data, many of them crosscutting in nature, to adequately answer the questions and provide informed choices to decision makers.

CONTEXT OF CURRENT PRACTICES

Good transportation has long been recognized as an important element of a successful society—from the Roman roads, which helped unite an empire, to farm roads, which help bring products to market. Moreover, the physical development of a community has been shaped by the transportation technology that existed during each growth period, whether it was canoes, horsecars, or freeways.

The importance of transportation to the economy and society has given transportation decisions great significance and those who make them great power. The importance of the central government in transportation decisions was debated during the formative years of the United States, and transportation continues to be an important function of federal, state, and local governments. The transcontinental railroad was seen as an important factor in unifying the United States after the Civil War, and the Eisenhower Interstate Highway System in the 1950s reshaped population patterns and goods distribution to both a domestic and a world market.

This history would suggest the evolution of a highly sophisticated practice, beginning with the transportation studies of the 1950s in Detroit, Chicago, and other metropolitan areas, and concurrent with the early development of computers. For example, the algorithm needed to calculate the shortest path through a network or to estimate traffic flows was borrowed from early research on telephone networks. Once transportation planning moved beyond understanding current travel patterns (which could be estimated though travel surveys) into projections, data needs escalated quickly.

In his review of the history of transportation planning, Weiner points out that “through its evolutionary development, the urban transportation planning process has been called upon to address a continuous stream of new issues and concerns, methodological developments, advances in technology, and changing attitudes. The list of issues included safety, citizen



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