When it comes to advertising, Gary Wakstein has tried it all. Over the past six years, the founder of Dinegift.com, a Needham, Mass., company that sells gift certificates good at more than 100 local restaurants, has bought newspaper ads, recorded radio spots, produced television commercials, mailed postcards, and more. But nothing provided the breakout performance Wakstein was looking for. So last fall, while preparing for the crucial holiday season, he tried something different. Scraping together $18,000--about 12% of his annual advertising budget--Wakstein leased a billboard.

The 14- by 48-foot, full-color image of a Dinegift gift certificate faced the eastbound lanes of the Massachusetts Turnpike for two months. As Boston-bound commuter traffic inched by, the sales poured in. Dinegift finished the holiday season up triple digits, and Wakstein says the "in-your-face" ad move was the clincher. "Newspapers didn't work for us, and TV was okay," he says. But when he combined his drive-time radio spots with the billboard and specifically targeted consumers in the car, it all came together. "That was the place they were ready to hear our message," he says.

Wakstein learned what a growing number of marketers are discovering: that the inside of the automobile is among the most fertile advertising territory out there. While consumers are blocking pop-ups, TiVoing through television commercials, and hanging up on telemarketers, they remain surprisingly open to a sales pitch while they're sitting behind the wheel. A recent study by Arbitron, the New York City-based marketing research firm, found that nearly 30% of consumers said a billboard or other roadside ad led them to visit a retail store within a week of seeing the pitch; 56% reported the same for a drive-time radio spot. And about half said they take notice of ads on the sides of buses, on bus-stop benches or kiosks, or atop taxicabs.

Marketers are revving their engines in hot pursuit. Steve Robbins, CEO of Robbins Bros. World's Biggest Engagement Ring Store, based in Glendale, Calif., uses a combination of radio and outdoor advertising to market his chain of seven southern California jewelry stores to marriage-minded men. He's done everything from traditional radio spots to mobile billboards--trucks plastered with his message that cruise the streets and freeways of Los Angeles and San Diego. He credits his on-the-road approach with helping Robbins Bros. double its market share, to 21%, over the past five years. Indeed, motorist-centered ads now receive 75% of the company's ad budget. It's the Zen of driving that puts the consumer in an open frame of mind, he says.

Some 30% of consumers said a roadside ad led them to visit a retail store; 56% said the same about a radio spot.

In fact, experts cite two reasons in-car marketing works so well. For one thing, during their morning and evening commutes, people switch on a kind of autopilot. Free from the regular multitask environments--even cell-phone chatting is forbidden by many state laws--clutter is reduced and ads have less trouble hitting their marks. Arbitron's research also found that on their way to work in the morning, consumers often are pondering their to-do lists; and on the way home, they often stop to pick up what they need. "They're in the car but they're in shopping mode," says Pierre Bouvard, president of new ventures for Arbitron. "They're literally making their mental lists. It's the window of opportunity right before they shop."

Even B2B marketers are hitting the road. The Castleton Group of Raleigh, N.C., is a provider of outsourced human resources services. When president Suzanne Clifton wanted to build name recognition, she opted for radio. Not with a jingle or pitch, but instead as the underwriter of a noontime current events talk show. She envisioned her target customer--a local senior executive--driving back from a morning meeting or on the way to a lunch gathering, with the car radio on. Six months after the radio sponsorship began, Castleton's sales staff reported that when they called on clients, about 65% of their prospects were familiar with the company. That was up from about 20% recognition last year. "When they're behind the wheel, stuck in traffic, people have time to listen," Clifton says. "There are fewer interruptions."

The ad industry is responding with more car-centric platforms. Night Agency in New York City can get your logo on a traffic cone or barricade. There's an outfit in Chicago that will paint your ad on a smokestack. And both Arbitron and Nielsen Outdoor plan to roll out new technology to better measure the reach of billboard ads, using global positioning satellite technology.

In the meantime, marketers are busy experimenting. Mark Chevrolet, an automobile dealership in Wayne, Mich., for example, is targeting consumers at the gas pump. For the past year, the dealership has been buying audio ads at local filling stations, which are broadcast through a speaker built into the fuel nozzle. The cost: $250 per ad per month. General manager Casey Cabana can't say for sure whether the spots have boosted car sales, but customers do tend to mention having heard them. And that's good enough for Cabana, who competes with 40 other Detroit-area dealers. "This is the most crowded market in the world for Chevy dealers," he says. "Every little bit helps."