A fundamental objection to many control system design techniques is that the possible inputs to a system are considered in a vague manner, if at all. Zakian has introduced a new principle of design, called matching, which uses a simple set theoretic approach and results in quantitative design criteria in terms of the inputs. The principle of matching gives rise to a design framework applicable to multi-criterion design problems, to which a solution can be sought by interactive numerical methods. This gives independent control over conflicting design criteria and the ability to specify the controller structure. A significant development within the design framework is the ability to model accurately complex inputs with both persistent and transient characteristics. This paper illustrates the modelling of complex inputs, and uses the principle to design a cheap, reliable and easily implementable add-on automatic speed control (sometimes referred to as ‘cruise control’) system for motor vehicles. The final design guarantees, for the plant model adopted, that for all possible inputs the system satisfies the conflicting design criteria, which are that the speed stays within its prescribed margins and that the vehicle travels within acceptable margins of ride comfort.