Use of On-Board Tailpipe Emissions Measurements for Development of Mobile Source Emission Factors

Advances in technology in the last few years have resulted in the availability of a variety of equipment for on-board measurement of highway vehicle tailpipe emissions during actual driving. As an example, NC State has recently completed a two-year study of the effect of changes in traffic signal timing and coordination based upon before and after measurements of vehicle emissions on selected corridors. This paper focuses on the key facets of experimental design for an on-road emissions measurement study using portable instruments and how the experimental design can be developed for various study objectives. Key elements of study design include vehicle selection, driver selection, route selection, instrument deployment, scheduling, and measurement of observable but not controllable factors that might influence emissions. The data collected from on-board instruments can facilitate the development of micro-scale, meso-scale, and macro-scale emission factors and emission inventories. Results from work at NC State are used to illustrate the major elements of study design and the potential uses of data. For example, speed and emission traces were used to identify emissions hotspots. Measured data were analyzed to estimate emission rates for different driving modes (e.g., idle, acceleration, cruise, and deceleration). Measured data were used to develop average emissions estimates for roadway segments or routes. Lessons learned from experience and recommendations for future work are provided.