Is it possible to model junction types such as signal-controlled intersections, roundabouts, priority junctions or merges in Vissim?

Any junction geometry can be modeled (signal-controlled intersections, priority junctions, merges including any type of roundabout) in Vissim.
The basic element of Vissim networks is a link (stretch of road) with one or more lanes. Links can be modeled exactly according to the geometry of the real junction with a precision down to one millimeter. Based on the link structure, network elements such as signal heads, conflict areas, priority rules etc. can be defined.