Tony Sportiello and Albert M. Tapper’s new musical comedy On the Right Track invites audiences to ride the rails on a New Jersey Transit train carrying three couples who have three very different problems. Sensitively directed by Mauricio Cedeño, the show is not only entertaining but edifying. It also reminds folks that “sometimes the key to happiness is simply a matter of knowing which door you want to open . . . and which one you want to keep closed.”