As spectacular as it is, the Hoover Dam is the bane of automobile travel between Las Vegas and Phoenix. The most direct route, Highway 93, literally takes you over the dam when you cross the border. It involves switchbacks down to the dam and then, depending on the time of day, you'll likely be slowed down by the tourists that are walking across it. Since 9/11, there has also been heightened security so you are slowed down by the check-points.
That's why the Colorado River Bridge is being built over the canyon. When completed, it will be a 2,000 foot long bridge nearly 900-feet above the Colorado River. I imagine it will clip about 30-45 minutes off of an average trip between Vegas and Phoenix. I also suspect it'll get some honorable mention in the "concrete arch bridge" chapter of some civil engineering textbooks too.
Some of our very good friends live in Vegas so we drive out there at least once a year and have watched the project develop over the past 4 years. This last trip we saw some significant progress and took a number of pictures for posterity. In 20 years when our girls are making the trip to Vegas we'll be able to pull out our digital photo album and say things like, "Your dad and I remember the days when you had to drive across the dam, up hill, both ways. And gas was only $2.51 a gallon."


