Monitoring in the data center can be expensive especially if you use proprietary technologies. Jalopnik has a post on a Bluetooth MAC address approach to use mobile devices in cars vs. a much more expensive automotive solution.
How Houston uses your Bluetooth phone to fight traffic
Anonymous Wireless Address Matching (AWAM) takes the individual MAC address on Bluetooth-enabled systems like phones, hands-free devices, computers, and even Sony PSP Go gaming devices and tracks them as they enter a roadway equipped with a sensor.
If you've got your iPhone in your pocket and you drive along Interstate 45 leaving downtown Houston the system records a version of your MAC address.
When you cross another sensor it records you again, recognizing you as the same vehicle. It then takes your speed between the two points and averages it with everyone else passing through the same two points.
This new approach provides Houston with a cheaper, more accurate, and more detailed traffic view than other car monitoring systems such as Automatic Vehicle Identification (AVI) technology, which the region also uses to monitor traffic.
"[AWAM is] dirt cheap!" said David Fink, with the Texas Department of Transportation Houston District. "If our current multi-lane AVI sensors cost $75,000 on the cheap end to install, the most expensive version of the AWAM with solar power and Wi-Fi costs $8,000."
Here is a PDF of the system.