单选题 Assuming that a constant travel-time budget, geographic constraints and short-term infrastructure constraints persist as fundamental features of global mobility, what longterm results can one expect? In high-income regions, (61) North America, our picture suggests that the share of traffic (62) supplied by buses and automobiles will decline as high-speed transport rises sharply. In developing countries, we (63) the strongest increase to be in the shares first for buses and later for automobiles. Globally, these (64) in bus and automobile transport are partially offsetting. In all regions, the share of lowspeed mil transport will probably continue its strongly (65) decline.
We expect that throughout the period 1990—2050, the (66) North American will continue to devote most of his or her 1.1-hour travel-time (67) to automobile travel. The very large demand (68) air travel (or high-speed mil travel) that will be manifest in 2050 (69) to only 12 minutes per person a day; a little time goes a long way in the air. In several developing regions, most travel (70) in 2050 will still be devoted to no motorized modes. Buses will persist (71) the primary form of motorized transportation in developing countries for decades. (72) important air travel becomes, buses, automobiles and (73) low-speed trains will surely go on serving vital functions. (74) of the super-rich already commute and shop in aircraft, but average people will continue to spend most c their travel time on the (75) .