This entry follows a similar one from my participation to the First Edition of CreateTheFutureContest.
The original concept of safety of travellers is the driver but the implementation is different.

BASIC CONCEPT
The basic concept is to identify trains, locate and track them and verify if two trains are running in opposite direction on the same SINGLE track (potential collision)

IMPLEMENTATION DESCRIPTION
A community of travellers, provide their GPS data to a Service Center.
The centre collects anonymous positions that are filtered based on their common speed, direction and movement.
Points (travellers) are associated in a cloud and the cloud is associated to a potential train, based on timetables and position.

TRAVELLER PRIVACY PROTECTION
When a traveller enters a space of few metres around a station, it receives a random code. The code will be used to correlate information from the same source. When the traveller leaves the station area he will be abandoned.
Only the code and the GPS data will be processed by the system.

POTENTIAL COLLISION DETECTION (not a rare event, unfortunately)
When two trains are seen moving in opposite directions on the same track, between two adjacent stations, a warning can be generated by the system and sent to the users.
No guarantee can be offered of correct identification of t risk and no authorisation is given to use this information to launch an alarm. No responsibility shall be assumed for anyone activating emergency brakes upon receiving the alert.
Anyway, being informed, could make you aware of a risk and let you make your own decisions.

TRAIN DRIVER, PRIVILEDGED TRAVELER
A train driver can be associated with special codes that must be requested by the Authority. Using these special codes, a driver can identify himself and the train he is driving. This will easy the train identification and allow the correct tracking of the train, his delays, time to arrive, real position along the line, etc.

SIMPLE CONCEPTS CAN PROVIDE USEFULL INFORMATION AND EVEN SAVE LIVES
The concept of clustering several travellers and use the points clouds to identify a train is based upon the concept that, statistically, if a lot of GPS sensors are moving along the limited space of train path, all at the same time, at the same speed, in the same direction, at a speed much higher than a walking human....they should be on the same train

PICTURE
This picture has been generated after a train detectable crash in Sardinia (Italy) 2010. It shows a potential map a symbols used for train representation.

THANKS FOR THE ATTENTION