What proponents of autonomous vehicles don't realize is that the only way to safely replace human judgement is to add such large margins of safety that the system you're automating is actually less efficient in an automated state than it was in its "human" state.
In the example you used, the merging process wouldn't be a problem because that two autonomous vehicles would be traveling about half a mile apart ... at a speed of about 25 mph. I'm only half kidding about that.
I’d argue that the only way to safely replace human judgement is for -every- vehicle on the road to be autonomous, and for the road to be completely isolated, ie: free from all human activity. Some swarm-based algorithms that could operate solely on distance-to-collision, with no regard to stripes, signs, contruction, etc. The movie Minority Report showed something akin to this.