How is the London Underground going to track riders?

Transport for London (TfL), which operates the London Underground subway system also known as the Tube, has found a new way to monitor rider habits and routes. Beginning in July, it will track passengers’ cellphones while they ride using the phones’ MAC addresses.

Every phone has a unique MAC address, which it sends to Wi-Fi access points in order to connect. TfL will start monitoring the locations of these MAC addresses, which will be tokenized so that they can’t be traced back to the phone, while on the Tube to get a better understanding of crowd levels and how to improve the system.

TfL will not be able to collect data from the phones like browsing history. Users can opt out by simply turning off the Wi-Fi on their devices while on the Tube.