The solution are based on the fact that 10-15% of all cars have a traceable Bluetooth device onboard. A Bluetooth device has unique ID, which can be tracked from sensor to sensor without any user involvement. A single sensor may cover both sides of a multilane freeway.
Alternatives
It’s also possible to collect information about traffic using more traditional methods.
GPS based Traffic Prope with backhaul cellular connection is good in terms of unrestricted coverage, but in practice is really difficult to reach a penetration of 3% of all cars which is required to effectively support real-time traffic monitoring on freeways (Journal of Intelligent Transportation Systems).
Cellular based Traffic Probe is also good in terms of unrestricted coverage, but its doesn’t provide accurate driving times.
Traditional road sensors, such as embedded loops and road side sensors are expensive and provides only a spot measurement, which makes them impractical on road segments with varying speed, such as freeways with queues.
Automatic Number Plate Recognition (ANPR) system can be used to measure driving times on a road segment, if at least two sets of cameras are deployed. However ANPR systems are expensive, difficult to deploy, and have difficulties in certain critical conditions such as “bumper to bumper” traffic, snow, fog or construction work where lanes are moved.
Conclusion
Bluetooth works like an ANPR system for measuring driving time on a road segment. The Bluetooth id is the "number plate" and can be read out from a Bluetooth sensor. A Bluetooth sensor is easy to deploy, covers easily both sides of a multilane freeway and it provides quality data under all possible conditions.
10-15% of all cars can be tracked providing a very comprehensive data set.
Bluetooth is a very competitive technology for monitoring traffic.