Using bluetooth signals to monitor traffic speeds/flow has been a thing for over a decade, and remains far cheaper than cameras. https://www.smatstraffic.com/b

Using bluetooth signals to monitor traffic speeds/flow has been a thing for over a decade, and remains far cheaper than cameras. https://www.smatstraffic.com/blog/bluetooth-and-radar-traffic-sensors-a-practical-guide-for-travel-time-speed-and-count-data-collection https://www.smatstraffic.com/blog/bluetooth-and-radar-traffi... "They detect Bluetooth or Wi-Fi signals emitted by mobile devices inside passing vehicles and capture the device’s MAC address, a unique identifier that allows the same device to be recognized at multiple locations"