In London, using a registered Oyster Card will allow Transport for London to know your exact route patterns (as long as you actually tag your card). Counter-terrorism programs in the capital city want access to the millions of Oyster touch-in/touch-out records, seeking patterns of behavior that match terrorist suspects. Currently, security programs can only ask for the records of specific individuals. The introduction of a Parisian transport smartcard (known as the Navigo), which requires personal information of the user and a passport size photo, has also posed concerns for civil liberty groups.
All metros have some sort of transit ticket that does not require giving personal information. But are they really anonymous? Chicago Transit Authority had tracked down the attempted kidnapping suspect through his 7-day pass (and security cameras), which does not require any sort of rider registration what-so-ever.
Debate still continues on whether one should be concerned about the police's access to transit card information.
Read post at 'Big Brother Is Watching Your Travel Habits'