During elevator modernization, a cross-dispatching system receives hall calls and assigns each hall call to either a group of existing elevator car controllers or a group of new elevator car controllers. The cross-dispatching system creates an inter group relative system response (iRSR) value for the hall call for both the existing group of elevators and the new group of elevators, based upon information from each group such as car location, in-service status, load, and direction. If the group assigned the hall call does not answer the call within a redispatch time period, the cross-dispatching system again calculates the iRSR for each group and reassigns the hall call.