From the What is BT website:
Research indicates that the average car shopper is in-market anywhere from 8 to 12 weeks from the moment they become in-market to the time they make their vehicle purchase. During this time, car shoppers spend roughly less than 3% of their total online time actually conducting research. That means 97% of their time online is spent on non-automotive research sites.If you have questions about behavioral targeting and want more information, the site has a nice BT resource reading list. Or you may view a collection of articles on BT from CoolAdzine for Marketers.