Judging by the experiences of Japan and France, both of which have mature high-speed rail systems, it would end the expansion of regional airline traffic as in-state travelers increasingly ride the fast trains. And it would surely slow the growth of highway traffic. Other potential benefits are also intriguing: a probable economic windfall for several cities along the route, with rejuvenated neighborhoods and center cities; several hundred thousand jobs in construction, manufacturing, operations and maintenance; and the environmental benefits that come from vehicles far more efficient and far less polluting than jets, buses and cars