Regardless of the billions spent on marketing and promotion, all the ads on radio and TV, all the efforts to create brand loyalty, the major chains must live with the unsettling fact that more than 70 percent of fast food visits are “impulsive.” The decision to stop for fast food is made on the spur of the moment, without much thought. The vast majority of customers do not set out to eat at a Burger King, a Wendy’s, or a McDonald’s. Often, they’re not even planning to stop for food — until they see a sign, a famili