Transit Bus Engine Power Simulation: Comparison of Speed-Acceleration-Road Grade Matrices to Second-by- Second Speed, Acceleration, and Road Grade Data

摘要

The Georgia Institute of Technology (Georgia Tech) School of Civil and Environmental Engineering has been developing speed-acceleration-road grade matrices for use in modal activity-based emissions models. These new modal emission rate models for heavy-duty transit buses predict emissions as a function of engine power demand for given transit bus activities, vehicle hours of travel, and baseline grams/brake-horsepower-hour emissions rates. Such models can predict the second-by-second emissions from a transit vehicle, given the vehicle characteristics, infrastructure parameters, and onroad operating conditions. However, one concern modelers are facing is the extent to which the use of more aggregated speed/acceleration parameters (rather than the second-by-second parameters) will affect model predictions. Hence, the goal of this evaluation is to assess the potential effect that the use of speed-acceleration-road grade probability distribution functions will affect predictions used in emissions inventory development and microscale air quality impact assessment. The research team developed a transit bus engine power demand simulator (TB-EPDS), which estimates transit bus power demand for given speed, acceleration, and road grade conditions. Speed-acceleration-road grade matrices were developed from speed and location data obtained using a Georgia Tech Trip Data Collector (an onboard computer with GPS receiver, data storage, and wireless communication device). Georgia Tech Trip Data Collectors were installed on two transit buses operated on numerous routes by Metropolitan Atlanta Rapid Transit Authority in Atlanta, Georgia. The TB-EPDS was used to estimate transit bus engine power demand using second-by-second data as well as using speed-acceleration-road grade matrices for each link and for the entire bus route. The researchers conclude that speed-acceleration-road grade matrices at the link level or the route level are both acceptable for regional inventory development. However, for microscale air quality impact analysis, link-based matrices should be employed.