Automakers count on them to create a positive buzz that will rub off on the rest of a product line, boosting showroom traffic. But a new study -- released last week -- suggests so-called "halo" vehicles are not always successful in creating much-needed glow for a brand, according to the Detroit News. Indeed, it's hard to quantify how the "halo effect" affected sales elsewhere in a brand's portfolio, according to the analysis by Northville-based CSM Worldwide, an auto industry forecaster. An example is the Volkswagen Beetle, reincarnated in 1998 with global fanfare. Volkswagen AG's U.S. sales that year increased 51 percent. Eighty percent of that increase came from Beetle sales -- with VW's remaining incremental sales of just under 14,000 units, scattered among the rest of the German automaker's offerings, putting into doubt the Beetle's halo effect, according to Mike Wall, who wrote the analysis. DaimlerChrysler AG's Chrysler brand saw a bump in its 2000 sales after the introduction of the retro looking PT Cruiser, but it was relatively short-lived, the News said. Some of the other more successful halo vehicles in recent memory include the Hummer H2, Nissan 350Z, and a perennial halo -- the Chevrolet Corvette. "What makes a good halo vehicle is any way to differentiate it from a mass market execution," Wall said. For halo vehicles at the upper end of the price scale, they must also be "aspirational," meaning even consumers who can't afford them might make it a goal to one day acquire them, says Wes Brown, an analyst with Los Angeles-based Iceology, a division of market research firm Nextrend.