My 2017 A4 Prestige come with both, the Adaptive Cruise Control and Traffic Jam Assist. Both features also use the Lane Control Assist. However, I still have to figure out the real difference, and WHY the actually offer both options. ACC accelerates and decelerates, stops and goes in all speeds. The TJA does the same thing, only. In lower speeds. So why is there a traffic assistant and what is really the difference. I can't seem to figure it out.

 

The TJA (from reading online) seems to basically lock onto the car in front of you and will follow it:

Audi A4 traffic jam assist

Another function of the ACC, the traffic-jam assist, can take over steering at speeds of up to 65 km/h (40.4 mph) on well-developed roads when traffic is congested. The system uses the radar and ultrasound sensors as well as the front camera, guiding the car by gently adjusting the steering and following the traffic ahead within system limits. In doing so, the traffic-jam assist uses the lane markings and other vehicles on the road for orientation.

https://www.audi-technology-portal.d...-jam-assist-en