I actually think they will do the reverse. A self-driving car will likely do more miles. What's more, it will do empty-passenger miles. The travelling patterns of people are unlikely to change. But there remains the distinct possibility that people will get their cars to drive to work, then home (or at least to remote parking) again if 'work' does not have parking.

Thus the potential for cars without people driving around. This is inherently worse for congestion than 1-person cars.