Here's What Transport for London Learned From Tracking Your Phone On the Tube (Gizmodo UK)
Later last year, Transport for London (TfL) collected wifi data from commuters' phones. This Gizmodo article shines light on a bunch of aspects of the data collection program, including:
Informing the commuters: TfL let commuters know about their wifi data being collected through posters, and clarified they won't identify individuals or collect their browsing history.
Route tracking: At the moment, TfL can tell what station you started and ended your journey at based on your Oyster card - but it can’t tell how you got between two locations. By using Wi-Fi data, merged with aggregated Oyster and Contactless ticketing data TfL has a far richer data source to ensure optimal and evidence based decision making for a wide range of planning decisions.
In-Station tracking: It isn’t just travel across the whole network that can be tracked by wifi. It’s even possible to track your location within an individual station - presumably by working out which access point that you’re closest to - this can be used to analyze crowding, to staff stations optimally, and to monitor how long passengers have been stuck on trains or held outside of stations - and offer refunds!
Advertising Potential: Being able to estimate the footfall in different parts of each station - and even roughly how long you’ll be staring at each advert - means that they can offer differential pricing depending on how good each advertising slot is.