Count Gene Breeden’s truck-driving school in Boulder City among the many things that changed forever on Sept. 11, 2001. Breeden taught would-be truckers how to drive treacherous mountain roads on U.S. 93 across Hoover Dam, with its steep grades and switchbacks. If they could drive that, they could handle anything, he found. Within hours of the terrorist attacks that brought down the Twin Towers in New York and left a hole in the side of the Pentagon in Washington, Hoover Dam closed. When it reopened, no heavy trucks were allowed across.