For a particular type of vehicle, fuel consumption and pollutant emission rates are mainly a function of the vehicle's use (journey type, frequency, etc…), and of the vehicle's operating conditions (speed, engine speed, rates of acceleration, temperature conditions, etc…), and depend on both the traffic conditions and the individual behaviour of the driver. Thus, a realistic assessment of emissions, pollution reduction methods and the effectiveness of emission control technologies cannot be carried out without taking into account the actual operating conditions of the vehicles. For that reason, a project has been carried out as part of the EC DRIVE programme to measure engine and vehicle operating conditions during normal driving. 58 private cars were equipped with sensors and data acquisition systems to record details of their use by their owners, each over a period of about one month. Over 8,200 trips were monitored, covering more than 73,000 kilometers of travel, during which the vehicle speed, engine speed, temperatures and other variables were recorded at one second intervals.
The data obtained yielded very accurate information on the actual use of the cars, which provided a broad overview of normal European driving, covering aspects such as daily vehicle use, trip characteristics (trip length, duration, and so on), speed and accelerations used, engine running conditions (engine speeds, choke use, etc…) and thermal conditions.
Traffic conditions have been characterized through splitting recorded speed profiles into “kinematic sequences”, between successive stops. Factorial analysis and classifying techniques enabled the characterization of these sequences and the ways in which different sequence types were linked. A set of driving cycles for realistic emission measurements has then been drawn up using these data, by recombining real sequences, randomly selected in accordance with the results of the statistical analyses. These cycles represent the European traffic conditions and driving patterns, taking into account the influence of the vehicle type, driver's behaviour and geographical location, as well as the detailed records of engine operations.
This paper describes the statistical analysis of the vehicle operation data, and the development of the test cycles. The driving cycles are compared with standard test cycles. The main characteristics of European vehicle use and their influence on fuel consumption are described: short trips, accelerations and more generally urban traffic conditions caused significant increases in fuel consumption.