| Current research suggests that vehicle emission rates are highly correlated with modal vehicle activity and that specific instances of load induced enrichment may contribute a disproportionate share of motor vehicle emissions. Consequently, a modal approach to transportation-related air quality modeling is becoming widely accepted as more accurate in making realistic estimates of mobile source contribution to local and regional air quality. New vehicle modal emission rate models will assess emissions as a function of specific operating mode or engine load surrogates. These new models require that vehicle activity be input by fraction of time spent in different operating modes. However, the ability to realistically model microscopic on-road modal vehicle activity currently limits the implementation of these models. |
