It’s one of the great eye-rolling moments of life in New York: as subway riders try to jam onto a crowded train at rush hour, the conductor makes an announcement telling them to stay on the platform because “there’s another train right behind this one.”

To which most straphangers respond: Yeah, right.

Now, New York City Transit aims to counter that skepticism with a novel experiment at the Myrtle-Wyckoff Avenues station on the L line in Brooklyn. Beginning in December, officials will install a computer screen at each end of the platform showing a graphic representation of the entire L line and the location of every train on it. Waiting passengers can watch the trains move along the tracks as the data is updated every 15 seconds. That way, passengers can see for themselves if there really is another train “right behind this one.”

If the system works, and riders like it, it could be installed in other stations on the L line, said Greg Lombardi, the line’s general manager, who helped create the system. Ultimately it could be used on other lines as well.

“There’s no end to the possibilities,” said Wilson M. Milian, a director of technology projects at the transit agency. He said that the same information could some day be displayed on the Internet, so that riders could quickly check the location of trains before heading to the subway.