No they can't, not if you want them to be safe. The biggest problem we have with human drivers, most people will say, is that humans can't drive safely. And one of the biggest reasons that is is because we drive way too close to each other. In an urban environment, it is practically impossible to maintain safe following distance: someone will slip in and take that spot instead.

Sure you might say that they can communicate with each other--they can't, not in any reasonably close timeframe for infrastructure (say, the next 30 years) where cars have to assume that human drivers are still on the road.

A worse effect is that self-driving cars are more likely to strictly stick to rules of the road and safe driving than humans are: so longer following distances, slower speeds, strict right-of-way rules when trying to make a left onto a jammed road... I don't see how they're going to be better.