The increasingly important role of transportation and its environmental impact is given major emphasis in this curriculum unit for secondary students. Four purposes of this unit are to describe and show (1) the historical development of transportation in America; (2) the effect of current transportation practices upon the environment; (3) some transportation practices which could result in a healthier environment; and (4) the expected effect on the environment of transportation being developed for the future. A model summarizes the main ideas related to each of the purposes. A list of important concepts precedes the chapters. Individual chapters include (1) model of unit-transportation and the environment; (2) transportation network development; (3) early transport routes in America; (4) the railroad and its impact upon American transportation; (5) the role of motor vehicles in American transportation; (6) the impact of air travel upon American transportation; (7) transportation-related pollution; (8) the impact of transportation upon urban congestion; (9) transportation land requirements; (10) efficient use of existing facilities; (11) direct government control; (12) urban rapid transit; and (13) transport modes of the future. (Author/JR)