Fortune 500 automotive companies are not optimizing their Web sites  efficiently enough and lack visibility on the major search engines,  according to a study conducted by digital marketing agency iCrossing. The study, Search 500 Index: Automotive, looked at 116 automotive- related keywords that online searchers often use. People are searching for automotive information online, but in  general they are not finding some of America's largest corporations  in natural search results, the study said. Optimization is not only key for driving sales, but is also critical  to building awareness, positioning and protection of a company's  brand both online and offline, the study said. ICrossing, Scottsdale, AZ, analyzed position data for Google, Yahoo, MSN, Ask.com and AOL. Companies are ranked based on iCrossing's index, which considers the  value of natural s