New York's cash-strapped Metropolitan Transportation Agency -- the behemoth that oversees the operation of the city's subways, buses, and commuter rail lines -- has sold the naming rights to one of the busiest subway stops in Brooklyn, and may do the same with stations throughout the system.

Barclays (BCS) will soon add its name to the Atlantic Avenue-Pacific Street station in Brooklyn, a major stop where 10 subway lines and the Long Island Railroad converge. The hook: There are plans to build a huge housing development and sports complex nearby, boosting the area’s prestige -- and the number of people passing through the station each day.

If the Brooklyn project succeeds, don't be surprised if express stops on the West Side line become Starbucks (SBUX), formerly known as 14th Street station; General Electric (GE), formerly 33rd Street-Penn Station; or McDonald's (MCD), formerly 42nd Street-Times Square.

The possibilities are almost endless: There are 468 stations along the system’s 26 lines and 722 miles of track. Advertisers already turn the inside of the subway’s 6,400 cars into rolling billboards. So why shouldn't there be illuminated signs on the tracks saying: “This rat-infested hellhole brought to you by Clorox"?

Sponsored stations are hardly what the subway's creators had in mind. Opened in 1904, the subway was originally intended as an ad-free public space.

More than 100 years ago, when the subway was first introduced, its technology was as new and intriguing as the Internet would be in the 1990s. It was the Steam Age, and electric propulsion was as-yet unproven. At the time, there were no commercial power companies, so the Interborough Rapid Transit Company built what was then the world's largest generating plant on a spot overlooking the Hudson River.

Engineers had to devise new tunneling techniques and equipment to handle the city’s varied geology. But they got the outlines of the system so exquisitely right that today few of the 4.5 million daily riders give the subway a second thought on their way to and from work.