This photo shows the interurban trolleybus line, south of Sinuiju.
Notice that on the left, there is a long raised viaduct. This feature is not present anywhere on the currently known route from Sinuiju to South Sinuiju (Namsinuiju), but can be found accross the river from said line.
Thus, it seems that at some point, the trolleybus line was longer than currently known, and probably continued south to Ryongchon County.