It can definitely handle traffic jams like a champ, and would slow all the way down to a stop and get going again automatically. If it stops for a long time, like minutes, or someone walks in front of your car and is detected by ultrasonic sensors, it will say hold on the dash and requir you to tap the gas to resume going from a stop.
I would almost always activate auto steer as well in a traffic jam. It makes it so much more tolerable.