I've never actually seen this work in practice, so maybe i'm missing something: Isn't the overall flow of traffic defined by the speed of traffic within the narrow section? E.g. if the speed limit and actual speed of traffic in the one- lane construction zone is 45mph, how people merge prior to that point should be irrelevant. The same number of cars are going to get through at the same rate.
From my experience, the speed is most often lower at the merging zone then in the following stretch of road. So overall througput could be improved by a more strict merging regime.
There are a few other things in play: You get less of the wave-like behaviour from 2 lanes merging. That means fewer start/stops. If the line is long enough, it may also reach the previous intersection - with two lanes it gets much shorter, avoiding blocking other directions.
