I think a solution for this would be to have the "self driving" speed limit be 10-15mph faster then the normal limit on highways. Since driverless cars can react faster this wouldn't cause more accidents and it would allow driverless cars to keep up with traffic. Plus, if traffic slows there's nothing stopping the driverless car from slowing down as well.
Or even better, just set speed limits at realistic levels (around the 85th percentile of natural traffic flow) for everyone. That said, I assume the driverless vehicles would at least be programmed to exceed the speed limit if necessary for an emergency maneuver.
