The purpose of the program was to define, determine, and typify automobile driving patterns in terms of operating modes. Data were collected in five major metropolitan areas and subsequently combined to form an overall composite of urban driving patterns. Three surveyor vehicles were instrumented with digital data acquisition systems for use in the field. The 'chase-car' concept was utilized, whereby the instrumented vehicles were operated to emulate the driving patterns of various cars representing the traffic population. Operating parameters of vehicle speed, time, and manifold vacuum, together with various route descriptors, were obtained from the chase vehicle and recorded on magnetic tape for computer batch processing. The data were processed to identify and summarize the basic vehicle operating modes: acceleration, deceleration, cruise, and idle. Mode characteristics such as frequency of occurrence, total duration, average duration, and transition probability were defined in matrix form.