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This paper reports on the analysis of on-road vehicle speed, emission, and fuel consumption data collected by four instrumented vehicles. Time-, distance-, and fuel-based average fuel consumption, as well as CO, HC, NO x , and soot emission factors, were derived. The influences of instantaneous vehicle speed on emissions and fuel consumption were studied. It was found that the fuel-based emission factors varied much less than the time-and distance-based emission factors as instantaneous speed changed. The trends are similar to the results obtained from laboratory tests. The low driving speed contributed to a significant portion of the total emissions over a trip. Furthermore, 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 deceleration) were more polluting than the steady-speed driving IMPLICATIONS The emissions and fuel consumption factors used in Hong Kong were developed in the United States and Europe, but the driving cycle developed for Hong Kong indicated substantial differences from those in the United States and Europe. Therefore, the emissions and fuel consumption factors obtained in this study can be used to estimate vehicular emissions and fuel consumption in Hong Kong. To achieve more definitive results, more instrumented test vehicles could be used to measure on-road emission rates and vehicle operating parameters. The current study suggests that the acceleration and deceleration modes are more polluting than steady-speed driving modes. Moreover, low driving speed contributes to a high percentage of total emissions. Great emphasis should be placed on minimizing vehicle stops in urban areas to speed traffic and to smooth acceleration and deceleration. Traffic engineers should devise control measures to improve traffic progressions and thus the pollutant emissions per vehicle. modes (i.e., cruising and idling) in terms of g/km and g/ sec. These results indicated that the on-road emission measurement is feasible in deriving vehicle emissions and fuel consumption factors in urban driving conditions.

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This paper attempts to propose a framework on driving cycle development based on a thorough review of 101 transient driving cycles. A comparison of the driving cycles highlighted that Asian driving is the slowest but most aggressive while European driving is the fastest and smoothest. Further review of the cycle development methodologies identified three major elements for developing a driving cycle; test route selection, data collection and cycle construction methods. A framework was eventually proposed based on these findings and recommendations from this review. First, traffic activity patterns and quantitative statistics should be considered in determining the test routes. Speed data can be collected by using chase car method, on-board measurement techniques or their hybrid. As for the construction of driving cycle, the matching approach has been more commonly used. It is recommended that the tendency of zero change in acceleration, which has been commonly ignored in the literature, and the application of succession probability at second-by-second level should be further explored. A fifth mode, creeping, is also recommended for modal analysis for characterizing urban congested driving conditions.

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