Transportation demand management, traffic demand management or travel demand management (all TDM) is the application of strategies and policies to reduce travel demand (specifically that of single-occupancy private vehicles), or to redistribute this demand in space or in time.[1][2]
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 and livable cities. TDM techniques link with and support community movements for sustainable transport.
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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.[3]
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.[4]
Some cities outside Europe have also consistently taken a demand management approach to transport and land use planning, notably Curitiba, Brazil, Portland, Oregon 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 1980–2000, it follows that (with a few exceptions) the techniques of demand management were not widely or successfully applied during this period. Small-scale projects to provide alternatives to single occupant commuter travel were common, but generally were led from outside the mainstream of transport planning. However many of the techniques in the demand management toolbox were developed during this period.
The British Government's White Paper on Transport [5] marked a change in direction. In the introduction to the White Paper, Prime Minister Tony Blair stated that
We recognise that we cannot simply build our way out of the problems we face. It would be environmentally irresponsible - and would not work.
A companion document to the White Paper called "Smarter Choices" researched the potential to scale up the small and scattered sustainable transport initiatives then occurring across Britain, and concluded that the comprehensive application of these techniques could reduce peak period car travel in urban areas by over 20%.[6]
A similar study[7] by the United States Federal Highway Administration,[8] was also released in 2004 and also concluded that a more proactive approach to transportation demand was an important component of overall national transport strategy.
The need to manage travel demand has now become urgent for a number of converging reasons.
Oil prices have now passed the previous peak in 1980, and 95% of all energy used in transport is oil. Vehicle travel in the United States, which has been rising steadily since records began, began to level out before the fuel price increases and is now in decline.[9] Part of this decline is likely to be people making fewer trips, with potentially far-reaching economic and social consequences. Countries and cities where the car is one of many travel choices are more likely to prosper, as people can choose to drive less but are still able to travel by transit, cycle safely, walk to local shops and facilities, or choose to work or study from home.
Transport systems are responsible for 23% of energy-related greenhouse gas emissions, and are increasing at a faster rate than any other energy using sector.[10] Demand management is central to the effort to reduce greenhouse gas emissions from urban transportation,[11]
Increases in vehicle travel are linked to a range of health problems including poor urban air quality, road injuries and fatalities, and reduced physical activity. The World Health Organisation released a [12] in 2003, and stated that:
We are concerned that current patterns of transport, which are dominated by motorised road transport, have substantial adverse impacts on health.
The efficacy of expanded roadways in managing traffic congestion is increasingly under challenge. Much of the traffic on new or expanded roads has been shown to be induced.
A growing sustainable transport movement is mobilising public demand for investment in safer, more livable cities with a greater range of travel choices.
There is a broad range of TDM measures, including: