This raises so many privacy concerns. Why do you need to be GPS-tracked, potentially up to an entire day, even when you're not on a train (like grabbing lunch along the way, etc)? All that is required to calculate the exact price for a trip is the time scanned in to the first station and time scanned out at your last station, possibly with an intermediate station to determine the exact route taken. And this system already exists in the UK: Oyster and the pay-as-you-go system in Greater London. It also handles daily caps, peak hour pricing, and the pink Oyster pads to show you took a specific (cheaper) route. With far less impact on someone's privacy. Just roll out Oyster nationwide, instead of implementing a new system, that collects far too much data about someone. Plus you don't need a specific app for that, you can just use any bank card or digital wallet.Or look at systems like OV Pay in The Netherlands, which is very similar to Oyster in function, but nationwide.