Bus Stop Updates?

[Coggley]

I`m doing research for a project and am trying to find out how bus companies in the UK update the information at bus stops.I.E. how do they transmit the info about how long the next bus will be arriving at the stop you are waiting at? Does the bus transmit a signal at each stop that is relayed back to a central point then back to the bus stops.Do they use a radio frequency? Or is there some sort of RFID tag in each bus? Anyone work in this field who can explain how it`s done
Thanks in advance Coggley

[Huderon]

ummm ... Wouldn't it be a good idea to phone a few bus companies and ask them ? After all, they are the ones using the technology