When I go to my local bar, they scan the code on the back of my ID to ensure it's not a fake. At a bar down the road, they swipe it through a computer. Sure, they look at it to see the age and compare the picture, but the computer does the verification of it's legitimacy. We're already there.
Let me tell you about the state tracking you, since you're worried about your ID being tracked. You know those signs on the freeway that say "15 minutes to Taylor Street" or "25 minutes to I-94"? Nice and handy, you know if it says 20 minutes when it normally says 5, there's a traffic jam. You know how they get that info? I learned this recently while working for a client that was involved in those signs being installed in that area. They scan the Bluetooth on drivers phones, and time how long it takes for a unique phone to get from one sign to the next. The average of that is the time that gets displayed on the sign.
So don't worry about your ID being scanned. They already know where you are. But obviously they're not sharing the information real widely, since the police took three days to find the person who hit my car and drove off even though I told them the description of the car, the driver, and the license plate number. So there's a little comfort I guess.
I've done some research in this area. Most systems are based on small radar devices mounted to light poles along the freeway which measure vehicle speeds traffic volumes at critical points (some traffic lights use these too now to detect waiting vehicles). A less popular now (because of higher install/maintenance cost) but still in use solution is magnetic induction loops embedded in the freeway lanes, in pairs to allow for speed calculation. The times are then extrapolated from the speeds at critical points (major on/off ramps, junctions, etc). A newer and still somewhat cutting-edge technology is the use of longer-ranch omnidirectional radars that can observe traffic on a road for quite some distance.
One of the really neat things about the modern radar units is that they feed into some software processing that can automatically detect accidents and other types of unusual events and alert authorities.
I'm not saying that there aren't people using bluetooth, but I suspect it's a small minority. I would think that if a municipality wanted to track individual vehicles through an entire section they would be more likely to use LPR, because it's a well established technology and there's a lot of inertia in government purchasing (read: unwillingness to try new tech/manufacturers).
Edit: there's also the confusing issue of vehicles that are tracked by radio transponders - these are going to be voluntary participants though, the obvious groups being people with EZPass type toll transponders and semi trucks with weigh station prepass devices (which are rather similar to the toll system). I wouldn't be surprised if municipalities use this data for traffic observation because it's already being collected for other purposes.
Bluetooth is not a small minority. It's a huge business, and Trafficcast is one of the leaders in this. Their product is called BlueTOAD. They're signing contracts with governments left and right.
MADISON, WI October 18, 2010 - TrafficCast announced it has now finalized agreements with nine leading distributors of traffic signal and control equipment, enabling localized sales services and product support in forty-one states plus the District of Columbia for its innovative BlueTOADTM technologies.
MADISON, WI March 1, 2011 - TrafficCast International, Inc. today announced that Econolite Canada, Inc. will distribute its BlueTOADTM line of products, enabling localized sales services and technical support in the ten provinces and three territories of Canada.
Given that it takes ~four seconds to pair my stationary iPad with my stationary JamBox, I'm skeptical of this claim. I once worked on a project that involved using tick data collected from the thousands of induction loops embedded in California freeways. Despite the data being somewhat noisy and error-prone, it was not difficult to more or less accurately infer traffic flow from these counts. I had always assumed that this is how they produced those estimates, but this was about 6 years ago.
IIRC that typically just dumps the barcode/magstripe and compares the birthdate to whatever you're looking for (typically 18 or 21+). It doesn't go ask the state if the license is valid.
Let me tell you about the state tracking you, since you're worried about your ID being tracked. You know those signs on the freeway that say "15 minutes to Taylor Street" or "25 minutes to I-94"? Nice and handy, you know if it says 20 minutes when it normally says 5, there's a traffic jam. You know how they get that info? I learned this recently while working for a client that was involved in those signs being installed in that area. They scan the Bluetooth on drivers phones, and time how long it takes for a unique phone to get from one sign to the next. The average of that is the time that gets displayed on the sign.
So don't worry about your ID being scanned. They already know where you are. But obviously they're not sharing the information real widely, since the police took three days to find the person who hit my car and drove off even though I told them the description of the car, the driver, and the license plate number. So there's a little comfort I guess.