请同学们阅读以上斜体加粗部分文字 ,朗读出来,附上音频或视频 Meanwhile, public policyplaces a number of constraints on the transportation system, which may be seenin some cases as diminishing its economic efficiency. The most obvious of theseare constraints related to environmental concerns, in the broad sense ofanything that impacts the “human environment”. In the United States, state andfederal laws not only establish a framework for evaluating the environmental impactsof transportation projects, but also establish numerous specific rules about whatcan and cannot be done.