How much will people travel in the future? Which modes of transport will they use? Where will traffic be most intense? The answers are critical for planning infrastructures and for assessing the consequences of mobility. They will help societies anticipate environmental problems such as regional acid rain and global warming, which are partially caused by transport emissions. These questions also lie at the center of efforts to estimate the future size of markets for transportation hardware--aircraft, automobiles, buses and trains.

In our research, we have tried to answer these questions for 11 geographic regions specifically and more generally for the world. One of us (Schafer) compiled historical statistics for all four of the principal motorized modes of transportation-- trains, buses, automobiles and high-speed transport (aircraft and high-speed trains, which we place in a single category because both could eventually offer mobility at comparable quality and speed). Together we used that unique database to compose a scenario for the future volume of passenger travel, as well as the relative prevalence of different forms of transportation through the year 2050. Our perspective was both long term and large scale because transport infrastructures evolve slowly, and the effects of mobility are increasingly global. The answers to those fundamental questions, we found, depend largely on only a few factors.