According to Audi,
The traffic jam pilot manages starting, accelerating, steering and braking. The driver no longer needs to monitor the car permanently. They can take their hands off the steering wheel permanently and, depending on the national laws, focus on a different activity that is supported by the car, such as watching the on-board TV.
Like other semi-autonomous vehicles that are available right now, drivers will still need to be readily available. Sorry, but you can't close your eyes and take a nap just yet. If the system "reaches its limit", the driver will be asked to return to the wheel and take over once again. I'm assuming "reaching the limit" is referring to the speed of traffic picking up, rather than the system overheating, freaking out, and shutting down. I could be wrong though, so who knows.
Either way, this will still require testing and I have no idea how the car performs in a real-world environment. Audi is a very reputable brand and I'm sure that they will make sure the system is put through all of the necessary tests before it gets in the hands of the consumers.