Do you think more people would share rides if cars could drive themselves? If this wouldn't be the case, I can see how the technology would help parking congestion but not how it would help traffic congestion.
Having smaller cars would actually be a good thing in that it would reduce the space wastage without changing the number of occupants. Don't know if you'd count that as technology in the sense of self-driving cars, though.
Self-driving cars can help traffic congestion in the sense that, if you can tell your car you don't care how long it takes to get somewhere, it might route you through a longer path and consequently help rebalance the load. Maybe.
This seems intuitively true but isn't. The majority (90%) of the space taken by a car at highway speeds is actually due to the buffer zone around it due to speed and not the size of the vehicle itself. Smaller cars don't increase highway throughput appreciably.
Maybe not carpooling, but proponents of self-driving cars often talk about how their efficiency (i.e. algorithmic efficiency in how they drive) would greatly ease traffic congestion. Much of the issue with traffic is just bad drivers (inefficient merging, accidents causing backups to name a few examples) but also current traffic controls like stop lights could essentially be removed if cars could reliably communicate with each other.
