The Ohio Department of Transportation has released a report that explains the development of a Bluetooth device capable of recording the media access control addresses of target radios on an interstate and then calculating the resulting space mean speed.
Full report [pdf]
Idea: Let’s line highways with Bluetooth sensors to pick up Bluetooth signals from phones/GPSs/devices as cars drive by, so that we can produce accurate travel times.
This has privacy implications despite what they say: “The MAC address is a unique identifier assigned during manufacturing of each Bluetooth target radio and is not associated with any personal information of a passing motorist; because of this, collection of data poses no threat to personal privacy.” There is a direct mapping (in most cases) of a Bluetooth address (BD_ADDR) to a user.
This system is probably also vulnerable to the known Bluetooth security vulnerabilities.
It sounds like this system picks up discoverable Bluetooth addresses, which modern phones keep off by default. The report implies that the system can pick up signals from phones paired to in-vehicle audio systems, but that requires the system to be able to detect and follow piconets (personal area networks), which is sketchy.