There will be traffic due to obstructions but it has been shown in many studies that even unobstructed traffic will result in traffic jams. The latter will absolutely be resolved with autonomous cars.
If autonomous cars reduce traffic-light response from 3s to 3ms there may be some temporary improvement. But a 3ms delay is still a delay and as traffic speeds and volume increase this delay will again become problematic.
The realities of physics ensure that there will always be a delay and it will always lead to congestion as the pipe fills.
We route internet packets at around the speed of light and still experience traffic congestion on those networks.
