It is easy to see how Roadify could be useful. But it is the kind of service that gets better as more people sign up, and it has not reached critical mass. It is not uncommon to click on, say, the E train at Queens Plaza, only to find an update saying the station is crowded — from six hours earlier. There is also some development work to be done: More than 20 bus lines have yet to be entered into the database, meaning that if you live in many parts of Queens, you’re out of luck. And the subway information is arranged by line, not by station. Trying to decide which train to take from Times Square? You have to check each line individually. Roadify is also largely nonfunctional underground, a serious shortcoming for something you want to use on the subway.