A situation where traffic stream A both opposes and is opposed by traffic stream B is a complex modelling problem. However, from OSCADY PRO v1.1, a mutual opposition model is included in the program, and this will automatically activate if a mutual opposition situation is identified.
Alternatively, you should either separate the turning movements out into separate traffic streams, or, if this is not possible, model one of the traffic streams as unopposed and reduce its saturation flow to compensate.