interestingly the NYC yellow cabs were recording all this data for a while and released it in an "anonymized" dataset, which turned out to be pretty easy to deanonymize because people tend to be picked up or dropped off near their homes or workplaces.

https://agkn.wordpress.com/2014/09/15/riding-with-the-stars-...

i think the answer is just that you don't have much meaningful privacy when using a taxi service in a normal way.