Advances in Computer Aided Testing technology to encompass laboratory simulation of service operations has allowed complete vehicle and component durability validation to be performed in the laboratory. During laboratory simulation testing the service loads experienced during proving ground or service operation are accurately and faithfully reproduced.A key part of the laboratory simulation test development process is the measurement and usage of the system model, or FRF (frequency response function). Conventional simulation techniques utilize a system model that incorporates an equal number of response transducers as there are control channels in the test system. This is sometimes called a square FRF. Techniques that utilize more response transducers than there are control channels (non-square approaches) have been in use for many years.Examples of the use of non-square simulation techniques on test control problems are described. An example of both square and non-square simulation results for a twelve channel full vehicle road simulator is presented to illustrate the non-square approach.