A Chicago "L" station is about the last place you would think of to pick up a carton of milk.

But online grocer Peapod has turned a busy CTA station at State and Lake streets into a virtual supermarket aisle, enabling commuters to use their smartphones to scan and buy any of 70 items.

Appearing overnight on once-barren walls, 7-foot-tall virtual shelves line both sides of a 60-foot tunnel, filled with everything from paper towels and diapers to fresh produce. Android and iPhone users can download a free Peapod mobile app to load up their electronic grocery carts for delivery the next day.

Chicago, Peapod's largest market, is the second U.S. city to roll out the interactive supermarket shelves, which first appeared last month at Philadelphia train stations. Other Chicago locations might be added, as well as locations in other cities, depending on what happens during a 12-week run at the station, which averages 17,640 commuters each weekday.

"It kind of changes the game for the out-of-home advertising medium, almost as a kind of service rather than branding," said Dave Etherington, senior vice president of marketing and mobile for Titan, a New York-based media firm specializing in out-of-home advertising, which created the campaign for Peapod.

The first virtual supermarket, a combination of advertising and retailing, was created last summer by British-based chain Tesco, which set up shop at subway stations in Seoul, South Korea.

Skokie-based Peapod took the idea as a promotional launching pad for its recent expansion into the Philadelphia market. In April, the interactive billboards were placed at 15 train station platforms across the city. The displays, which will be running through early June, were winnowed to nine locations.

Response to the ads has been strong, said Etherington, in terms of introducing the service and selling the items on-site to shoppers waiting to catch a train.

"It does a fantastic job of branding but in a very transparent, measurable way, it ships products and it generates revenue," Etherington said.

Peapod, founded in 1989 in Evanston, pioneered the concept of online grocery shopping, long before many people knew what the Internet was. The publicly traded company, perhaps ahead of its time, struggled during the dot-com bust and was acquired by Netherlands-based Royal Ahold in 2001.

Peapod serves 24 U.S. markets and has delivered 21 million grocery orders in slightly more than two decades.

With Internet shopping fully integrated into the retail landscape, the company introduced its first mobile app about a year ago, trying to get in front of the next wave in marketing. Used primarily by existing customers to reorder items, so-called trash scanning, the mobile app has new utility with the virtual supermarket billboards.

"Grocery shopping doesn't necessarily happen the way it used to," said Mike Brennan, senior vice president and chief operating officer of Peapod. "It's becoming more of a task that happens in multiple steps throughout the week."

The shelves were fully stocked Thursday at the Red Line Lake Street stop as the first wave of commuters perused the virtual supermarket aisle on their way through the station. Some swiveled, others stay focused on the light at the end of the tunnel, and a few stopped to shop.

Many commuters took notice of the realistic depiction of typical grocery store shelves. Items included Huggies Diapers, Bounty paper towels, Barilla ready-to-heat pasta and fresh produce such as apples and bananas. Like a real supermarket, shoppers might need to kneel slightly to select items from the lower shelves, but many won't need a stock boy to reach the top shelf with their smartphone scanner.

Making a purchase requires a smartphone and bar code scanner app. First, the shopper downloads a free Peapod app displayed on the wall. To buy requires pointing at the item and scanning its bar code, which shows the price, then checking out. Items will show up at the customer's door within a day.

Virginia Marino, 28, an attorney from the Wrigleyville neighborhood, was headed to her LaSalle Street office at noon, after working from her home during the morning. She glanced from side to side with interest as she made her way through the tunnel but questioned whether she would be able to shop during her normal commute.

"I typically take the 'L' during rush hour, so I don't know that I would take the time to really walk by with my phone and shop, because I'm trying to get home or I'm trying to go to the office," Marino said. "And there's no way you're stopping; because of the crowd, it's just not going to happen."

Brandon Precin, 23, of Evanston, a three-time All-American wrestler from Northwestern University, who usually goes shopping only after he has run out of food, was impressed with the impulsive nature of virtual foraging.

"I think it's really cool, being able to walk by, scan something and shop," Precin said. "That's a great concept. You get to look for what you want, scan with your phone and that's it."

Hurrying to class at Harold Washington College, Evelyn Ramirez, 20, of Chicago, slowed enough to take in the new ambience at the not-so-pedestrian tunnel. It was, if nothing else, an artistic success.

"It's kind of interesting," Ramirez said. "I feel like I'm actually in a store right now."

Peapod, which has relied mostly on direct marketing to draw customers, doesn't expect its new campaign to become a primary retail channel for the company. Although more locations might be in the offing, the logistics of a full virtual supermarket may be prohibitive, Brennan said.

"There's still only a limited number of products, no matter how many you put up on the billboard," he said. "Peapod has 12,000-plus products, and that would be a pretty long billboard to be walking down."

rchannick@tribune.com

Twitter @RobertChannick