According to Wikipedia the Hoover Dam Bypass refers to the construction of the Mike O'Callaghan-Pat Tillman Memorial Bridge and connecting roads for a new route across the Colorado River for U.S. Route 93. The project links the U.S. states of Nevada and Arizona by spanning the Colorado River 1,500 feet (460 m) downstream from the Hoover Dam. The entire project is expected to be completed by September 2010.
This was truly an awesome sight. I can't wait to drive over the bridge someday.