If the volume is disparate, then the road with less traffic can wait... kind of like a stop sign! Except the road with more traffic won't back up and cause massive problems.

If the traffic intensity of the main flow is so high, that there are never any gaps, then it is near the saturation and will cause traffic jams anyway. Which first needs to be fixed anyway and second will also cause gaps to be created again, because the main flow comes to a halt.