On-road motor vehicle emissions and fuel consumption in urban driving conditions

This paper reports on the analysis of on-road vehicle speed, emission, and fuel consumption data collected by four instrumented vehicles. Time-, dista nce-, and fuel-based average fuel consumption, as well as CO, HC, NOx, and soot emission factors, were derived. The influences of instantaneous vehicl e speed on emissions and fuel consumption were studied. It was found that t he fuel-based emission factors varied much less than the time- and distance -based emission factors as instantaneous speed changed. The trends are simi lar to the results obtained from laboratory tests. The low driving speed co ntributed to a significant portion of the total emissions over a trip. Furt hermore, the on-road data were analyzed using the modal approach. The four standard driving modes are acceleration, cruising, deceleration, and idling . It was found that the transient driving modes (i.e., acceleration and dec eleration) were more polluting than the steady-speed driving modes (i.e., c ruising and idling) in terms of g/km and g/sec. These results indicated tha t the on-road emission measurement is feasible in deriving vehicle emission s and fuel consumption factors in urban driving conditions.