The use of very short wavelength radar sensors for closed loop adaptive cruise control (ACC) and obstacle detection has been demonstrated as part of various international research and technology demonstration programs (e.g. PROMETHEUS in Europe). The first radar systems for distance measurement and target tracking are now under development, with vehicle trials already under way in several countries.This paper describes a 77 GHz radar sensor which will begin production next year (1999) as a headway sensor, initially for use in cruise control systems. The challenges facing the sensor manufacturer include the development of robust product designs and process technologies suited to the high volume and reliability demands of the automotive market, whilst achieving this at a sustainable production cost. The key design features of such a product are described, together with the major factors influencing cost and performance.