Impact of Traffic Conditions and Road Geometry on Real World Urban Emissions Using a SI Car

A precision in-vehicle tail-pipe emission measurement system was installed in a EURO1 emissions compliant SI car and used to investigate the variability in tail-pipe emission generation at an urban traffic junction and uphill/downhill road, and thereby the impact of road topography on emissions. Exhaust gas and skin temperatures were also measured along the exhaust pipe of the instrumented vehicle, so the thermal characteristics and the efficiency of the catalyst could be monitored. Different turning movements (driving events) at the priority T-junction were investigated such as straight, left and right turns with and without stops. The test car was run until hot stable operating conditions were achieved before each test, thereby negating cold start effects.

To demonstrate the influence of the junction and road geometry on tail-pipe emissions and fuel consumption, distance based factors were determined that compared the intersection drive-through measurements and uphill/downhill measurements with steady speed flat road runs. Fuel consumption was increased at intersections by a factor of 2∼4.1. CO, THC and NOx emission were increased by a factor of 1.8∼6.2, 2.5∼5.1 and 2.8∼7.5 respectively. Benzene emissions at intersections were also increased by a factor of 10∼20. The fuel consumption and emissions were lower and higher than flat driving for downhill and uphill driving, respectively. However, the combined uphill/downhill driving fuel consumption and emissions were notably higher than comparable flat road driving. Through fine-scale analysis of real-world driving profiles and tail-pipe emissions, this research makes a contribution to our understanding of the variability in driving parameters and emission production in urban areas. The results of this study will be useful in aiding the development of combined traffic/emission models for urban areas and developing optimal traffic management strategies to minimize emissions.