More than a third of all Americans hold passports. That's twice as many as in 2000. That doesn't mean Americans have developed a new taste for exotic and far-flung destinations. Think back to 9/11 and the resulting regulations that heightened security measures for travel. "Implemented in 2007 for air travel and on sea and land borders in 2009, [the Western Hemisphere Travel Initiative] required passports for U.S. citizens entering from Canada, Mexico, the Caribbean, and Bermuda," Andrew Bender writes.