An issue raised by the mathematical modeling of the ADL and USDOT telecommuting studies is the extent to which each model captures the full relationship of telecommunications and travel. Why is the number of vehicle miles traveled (VMT) growing so fast and urban traffic congestion increasing while telecommunications is growing in capability and use every day, and why does this occur while the number of telecommuters is growing in the short term at more than 10% annually (Exhibit 1-2)? One answer is that commuting represents a minority share of trip purposes, even in rush hours, as illustrated in Exhibit 1-3, and is growing smaller. Telecommuting can only do so much for vehicle miles traveled, as reflected in the conclusion of the USDOT report. Furthermore, telecommuting is not the only travel-related application or consequence of telecommunications. Telecommuting is embedded in a much larger span of telework, which in turn is only a portion of a larger complex of economic processes that are changing because of telecommunications.

Another issue is the extent to which telecommunications applications beyond telecommuting fail to provide substitution for travel overall. This could be because travel growth is mostly independent of telecommunications or because there are mechanisms whereby some travel is stimulated by telecommunications. These are mechanisms that we investigate in this study.

In an extensive body of published work that extends back to the early 1980s, Ilan Salomon has consistently argued against the conventional wisdom that telecommunications is a substitute for transportation. He notes in one study (Salomon, 1990), "There is, at present, very little evidence to support the substitution [of telecommunications for transportation] hypothesis." He writes in another paper (Salomon, 1987), "The findings [from an empirical study of telecommunications' impact on regional inequalities] suggest that reduced telecommunications costs do not have a major impact on changing the relative weights of location factors. The interplay of demand, supply and government intervention indicates that the disadvantage of distance will persist in the information era." The basic thrust of his work is that there is much more to be learned about how travel and telecommunications interact.

Patricia Mokhtarian (1990) of the University of California at Davis provides an initial framing for much of what is covered in this present study. Her work describes numerous ways in which telecommunications affects the demand for, and supply of, transportation, and vice versa. Many of them are elaborated upon in this study.

Rather than building up from the ultimately small phenomenon of telecommuting as a travel substitute, we take a top-down look at the U.S. economy and paint a larger picture of how telecommunications and transportation are working together both as substitutes and as complements. This present report focuses on and explores the apparent contradiction between the growing ability of telecommunications to substitute for trips through telecommuting and its effect in shaping a society in which travel per capita continues to increase year by year (Exhibit 1-4).

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