Trips may be made by differing methods or modes of travel and the determination of the choice of travel mode is known as modal split. In the simplest case when a small town is being considered the choice is normally between one form of public transport and the private car, with the car being used for all trips where it is available. In such a situation most trips on the public transport network are captive to public transport and very little choice is being exercised. In the larger conurbations however the effect of modal split is of very considerable significance and is greatly influenced by transport policy decisions.