A Methodology for Developing Transit Bus Speed-Acceleration Matrices to be Used in Load-Based Mobile Source Emissions Models

A physical-activity-based transit bus emissions model estimates emissions as a function of transit bus power demand for given transit bus activities and environmental conditions. Transit bus speed and acceleration rates are key activity parameters as well as the most important parameters in the estimation of transit bus power demand, also know as the engine load. Once the transit bus engine load is calculated for a given speed and acceleration, emissions in grams or grams/vehicle-hour can be calculated using grams per brake-horsepower-hour emission rates. To quantify Atlanta regional transit bus speed and acceleration rates, the Georgia Tech research team installed a Georgia Tech Trip Data Collector (consisting of an onboard computer, GPS receiver, a wireless communication device, and data storage) in a transit bus operated by Metropolitan Atlanta Rapid Transit Authority. The team collected second-by-second speed and location data for three weeks, and created speed-acceleration matrices by roadway facility type and by time of day. In this paper, the researchers focused on a methodology development to create transit bus speed-acceleration matrices in use of load-based modal mobile source emissions models for the Atlanta metropolitan area. Once a bus service route is specified by roadway facility type and by time of day, engine power demand for each matrix speed bin can be calculated, weighted by acceleration frequency fractions on each corresponding matrix bin, and then multiplied by emissions levels that can be obtained from engine dynamometer or chassis dynamometer test results. TRB 2005 Annual Meeting CD-ROM Paper revised from original submittal. Seungju Yoon, Hainan Li, Jungwook Jun, Jennifer Ogle, Randall Guensler, and Michael Rodgers 3