Previous research introduced the solution space as a workload metric for air traffic controller merging tasks. The solution space Diagram is a mapping of intruding aircraft trajectories to the velocity/heading plane in the form of conflict zones and safe areas. Choosing a velocity vector in either one will provide an unsafe or a safe solution, respectively. In this paper an improved, dynamic solution space will be tested for correlations with air traffic controller workload. An experiment has been conducted where subjects were required to line up all aircraft in a sector towards a certain waypoint, while continuously rating their workload. High correlations were found between several solution space parameters and the subjective workload.