02/01/2011 02:35 pm ET Updated May 25, 2011

SubwayArrival App Uses Commuter Location To Map Real-Time Schedule

We've seen it a thousand times.

Impatient passengers leaning over the edge of subway platforms, trying to catch a glimpse of the next train.

Alex Bell, a graduate electrical engineering student at Columbia University, says he has developed an app that will allow users to know when their next subway train is coming, in real time.

"The app does for ZERO DOLLARS what the MTA hasn't been able to do for $300 million," Bell writes in an email to HuffPost.

The catch? "To make this application a reality requires users in order for the system to provide data," Bell says.

In other words, much like the cab-sharing app we wrote about called Weeels, the app only works if lots of people opt in to use it.

SubwayArrival uses subway commuters' locations and generates the relative location of the train they've just rode on. "In short, the mobile phone looks for changes in base station ID, periods of no service, and large distances travelled. When all three of these criteria have been met the server know the user has emerged from a subway trip. This information is sent to a central server which compiles the information and displays to all users the current location of subways." The MTA has been rolling out countdown clocks, but they are currently only on numbered lines and the L.

Remember: it won't work unless you use it. Do you want to know where your subway is or not?

"SubwayArrival" is available on the iPhone and iPad. Download the free Subway Arrival app here.