Pairs of one way streets carry more traffic then when those two roads each have traffic going in two directions. There are less vehicles turning on the road and traffic signals can be timed to let larger platoons of traffic move through. This is why traffic engineers were busy implementing one way streets in major downtown districts throughout the United States in the first half of the twentieth century.
The problem with one way pairs is they provide less access to the adjacent parcels. They can also be less friendly to bicyclists and pedestrians because they carry larger platoons of automobile traffic. That is why the City of Minneapolis will be converting Hennepin Avenue and 1st Avenue North from one-way streets to two-way streets. Minneapolis' transportation plan (Access Minneapolis) also shows that the vast majority of one-way pairs need to remain to accommodate the traffic flow in and out of downtown.
