The valuable real estate in commuter hubs, seen by thousands of pairs of eyes a day, have attracted ads for everything from soft drinks to universities to plastic surgery.

But on Monday (June 17), passengers on New York-bound trains who happened to look out the window as they traveled between 14th and 23rd streets in Manhattan were greeted by an unexpected sight: an ad in the tunnel, according to the Jersey Journal.

And it was no ordinary ad.

This promotion, for Target stores, moved along with the train. Or at least it seemed to.

In fact, what PATH riders saw is called a motion picture advertising system. The colorful, 15-second display works like a flip-book: a series of images are placed side-by-side and as the train moves, it creates the illusion that the picture is moving as well.

Using hundreds of lights, the Target ad is like a very short film. Different people are pictured in various active or athletic settings, such as playing badminton, with the Target logo prominently featured.

With most other subterranean surfaces already in use as ad space, officials at PATH say the new display, which will be up for 12 months, may be the first of more to come.

"This demonstration project is a truly innovative concept that I believe will add a new dimension to customers' daily commute," said Michael DePallo, general manager of PATH.

It will also, no doubt, add some revenue to the system, which is managed by the bi-state Port Authority of New York and New Jersey. PATH officials declined to say how much they are receiving for leasing the tunnel space.

In a statement on its Web site, the advertising company that develops and maintains the ads, Submedia, said "in many cases, our transit authority partners will double their existing earnings from advertising" by using the motion picture system.

Submedia's co-founder and the developer of the technology, Joshua Spodek, said this type of ad can be used in any number of spaces where people move along a fixed route, such as airport walkways.

"Right now, (transit systems) have all this ad space and they're not doing anything with it," said Spodek, who has a doctorate in astrophysics and founded Submedia in 1999.

PATH already has plans to place a second ad on the wall of a Manhattan tunnel.

In a written statement, Target Corporation's vice president of events and communications, John Remington, called the tunnel wall "a novel medium for showing our brand in a fun and unique way."