Browse Publications Technical Papers 2006-01-3394

Development of a Driving Schedule to Mimic Transit Bus Behavior in Mexico City 2006-01-3394

It is difficult to project the emissions performance of a vehicle on a route unless the test cycle used to gain the emissions data reasonably represents that route. A chassis dynamometer emissions measurement test schedule consisting of three modes (congested, non-congested and bus rapid transit (BRT) operation) was developed for use in a program to evaluate transit bus technologies in Mexico City. Existing buses were fitted with global positioning system (GPS) data loggers and, between September 2nd and 8th of 2004, 54 hours of speed-time data were collected while the buses were operated over several bus routes in Mexico City. The data set was then broken down into individual micro-trips, each consisting of an idle period followed by the bus traveling some distance, followed by a final deceleration to idle. An initial attempt to categorize each micro-trip according to time-of-day and thus determine whether the micro-trip occurred during defined rush-hour and non-rush-hour periods was unsuccessful due a lack of correlation between congested conditions in Mexico City and time-of-day (i.e. there is no clearly defined and spatially extensive rush-hour). Hence, the researchers defined two operational modes, namely “congested” and “non-congested”, with the distinction that the congested mode would contain micro-trips with average speeds falling in the lower 75th percentile while the non-congested mode would contain micro-trips falling in the upper 75th percentile. As a result, two modes would have different average speeds, and permit projection of emissions over links with a variety of average speeds. With these definitions, and a reasonable mode length of 1000 seconds, an iterative computer process randomly combined the individual micro-trips from each mode to form forty driving schedules. Each schedule was then compared to the characteristics of the entire respective (congested, non-congested) data set and the schedule which matched the characteristics of each mode most accurately was selected.


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