If I recall my networks course correctly, a device's MAC address is publicly visible and never changed. If the car is broadcasting, it should be easy to log this MAC address and track the car across the city. If I'm mistaken about this, please correct me.

MAC address can be easily changed, with ifconfig(8). Nearly every Unix has an ioctl(2) request for this. So does NT.

But on mobile you might need a "rooted" device.

I have the following script in my OS X toolbox to allow me to connect to public WiFis for longer than allowed time.

  #!/bin/bash

  sudo ifconfig en1 ether `openssl rand -hex 6 | sed 's/\(..\)/\1:/g; s/.$//'`

IIRC this isn't "changing" the MAC address, as a reset of the software will once again begin broadcasting the original. Rather, it is spoofing, i.e. forcing the software to lie about the MAC address that was built into the hardware.

Yes, but it's not a constant, but more of a configurable option; change can be made trivially, and as often as needed.

Unix init scripts for networking can do MAC changes for you every time an interface goes up.

Only on it's local network. Unlikely that cars will set up dynamic local networks and talk to each other directly though. More likely they'll be assigned an IPv6 address by a service provider.

I'm still unclear about whether the EU "eCall" system (which requires cars to SMS their location to the emergency services in the event of an accident) will also have the car attached to a cell all the time.

Of course it will. You think governments won't take that opportunity to track you under the guise of "tracking bad guys"? The same applies to the insurance black boxes that some want introduced.

I can certainly expect that, but I'm looking for actual confirmation of how the system works / is supposed to work. It's not a "secret", it's just a piece of information that's hard to extract.

Of course! We all know why the toasters were able to wipe out the fleet. Because the battleships were able to talk to each other!

The goal is full-spectrum human tracking. Tagging cars is just an obvious step along the way.