You've heard of P2P, but have you heard of V2V?
Vehicle-to-Vehicle communications is, as the name implies, data exchanged between two vehicles. The NHTSA has announced that they are beginning to draft rules to "enable vehicle-to-vehicle (V2V) communication technology for light vehicles," and that eventually all new vehicles will be required to have V2V communication technology.
V2V communication wirelessly transmits bursts of "basic safety data" ten times a second. While there's no hard definition of "basic safety data" right now, it will include the speed and position of the vehicle.
V2V technology will be used to help prevent accidents. The current, tested implementation uses the safety data to warn drivers if there's a car coming. For example, if you are changing lanes, you will be warned if there's a car coming in the other lane. According to DOT research, V2V technology can prevent a majority of accidents that involve two or more vehicles. Right now, there are no plans for your car to take over; your car just warns you.
There are a number of privacy issues that are going to come into play on these future regulations, and there are some significant security issues too.
The NHTSA has said that anonymized data will be available to the public. It's fairly easy to identify individuals from such data, so people who have safety concerns about being tracked (such as those with restraining orders against other people) will need to be extra careful.
Vehicle manufacturers will also be able to collect additional information so long as the correct basic safety data is transmitted to other vehicles. The extra data can be used by your insurance company to determine your rates, and so on.
It also sounds like your vehicle will be tracked, though the information may be vaguely difficult to access due to this line: "vehicles would be identifiable through defined procedures only if there is a need to fix a safety problem."