On the northern intersection, there are vehicles stopped in the median waiting to turn. You may also notice there are stop lines in the median, encouraging this behavior.
In contrast, drivers travel through the southern intersection with a single maneuver. There are no stop lines, and no vehicles stopped in the median.
In order to model this behavior in SimTraffic, the southern intersection should be modeled as one intersection with a median. The northern intersection should be modeled as two separate intersections, that may operate on a single controller using the Cluster Editor.