In my opinion(I'm not a lawyer) it's better to ask forgiveness than permission. So market the app. Then, if the train company tries to harass you, take the app

In my opinion(I'm not a lawyer) it's better to ask forgiveness than permission. So market the app. Then, if the train company tries to harass you, take the app down and open source it. That way, you'll make money between the time you launch, and the time the train co notices you, and you'll have a great reference for your next project. And if they choose not to do anything, even better! Just make sure you back down when their C&D comes. No need spending all your profits on attorney's fees.