[phyphy]

Here in India we have an app named "Where is my train?". Local people use this app a lot when traveling by train. It's not government owned either and has no ads. Just throwing in here for some inspiration since I don't know the inner workings of that app.

Edit: It uses nearby cell towers to estimate the location of train

[Dharmaaa]

and In 2018 , Google has acquired Sigmoid Labs Pvt. Ltd, the team behind the “Where is my train”.

[rathish_g]

and integrated to Google Maps