While this is true, it only works where cameras are present, and adding a significant number of cameras costs time and money.

COTRAVELER[1] is much easier and costs almost nothing. Just having a cellphone in a car (either in the driver's pocket or "OnStar") - which only needs to be on and giving presence notifications to the local tower - is enough to get very accurate near-realtime tracking information. The only costs are read-only access to the tower logs and a few SQL JOINs.

[1] https://www.washingtonpost.com/apps/g/page/world/how-the-nsa...