The proposed approach started from an investigation of psychophysical stimuli relevant to the detection of a vehicle in an urban environment. Existing simulators were then evaluated from the standpoint of their capability of high fidelity reproduction of real stimuli and on their ability to handle virtual stimuli (i.e. from virtual vehicles). Sound Answers has followed an iterative approach to the development of a multi-modal detectability metric, by first conducting experiments of vehicle detection based on one type of high quality cue (as an example, just visual or audio or vibration). Bi-modal detection experiments would then be conducted by using the (one or more) simulators that offer best signal quality for at least two stimuli. The results of both experiments would be analyzed to derive a detectability model based on one stimulus only, then a detectability model which accounts for the cross-coupling among two stimuli at a time. Finally, a hypothesis of a multi-modal metric model was formulated along with a specification document for the simulator to be built in Phase 2.