Transportation demand management, traffic demand management or travel demand management (TDM) is the application of strategies and policies to reduce travel demand, or to redistribute this demand in space or in time. In transport, as in any network, managing demand can be a cost-effective alternative to increasing capacity. A demand management approach to transport also has the potential to deliver better environmental outcomes, improved public health, stronger communities, and more prosperous cities. TDM techniques link with and support community movements for sustainable transport. The Association for Commuter Transportation defines TDM as the use of strategies to inform and encourage travelers to maximize the efficiency of a transportation system leading to improved mobility, reduced congestion, and lower vehicle emissions. Background The term "TDM" has its origins in the United States in the 1970s and 1980s, and is linked to the economic impacts of the sharp increase in oil prices during the 1973 oil crisis and the 1979 energy crisis. When long lines appeared at gas stations, it became self-evident that alternatives to single-occupancy commuter travel needed to be provided in order to save energy, improve air quality, and reduce peak period congestion. The concepts of TDM borrowed from mainstream transport planning in Europe, which had never been based on assumptions that the private car was the best or only solution for urban mobility. For example, the Dutch Transport Structure Scheme has since the 1970s required that demand for additional vehicle capacity be met only "if the contribution to societal welfare is positive" and since 1990 has included an explicit target to halve the rate of growth in vehicle traffic. Some cities outside Europe have also consistently taken a demand management approach to transport and land use planning, notably Curitiba, Brazil; Portland, Oregon, US; Arlington, Virginia, US; and Vancouver, Canada. Relatively low and stable oil prices during the 1980s and 1990s led to significant increases in vehicle travel, both directly because people chose to travel by car more often and for greater distances, and indirectly because cities developed tracts of suburban housing, distant from shops and from workplaces, now referred to as urban sprawl. Trends in freight logistics, including a movement from rail and coastal shipping to road freight and a requirement for just in time deliveries, meant that freight traffic grew faster than general vehicle traffic. Because vehicle travel was increasing rapidly from 1980 to 2000, it follows that (with a