06 - 1096 Speed - and Facility - Specific Emission Estimates for On - Road Light - Duty

Estimating the emission consequences of surface transportation operations is a complex process. Decision makers need to quantify the air quality impacts of transportation improvements aimed at reducing congestion on the surface street network. This often requires the coupling of transportation and emission models in ways that are sometimes incompatible. For example, most macroscopic transportation demand and land use models such as TransCAD, TranPlan or TRANUS produce average link speed and link VMT (vehicle miles of travel) by vehicle and road class. These values are subsequently used to estimate link-based emissions using standard emission models such as EPA’s MOBILE6 model. On the other hand, recent research using Portable Emission Monitoring Systems (PEMS) indicates that emissions are not directly proportional to VMT, but are episodic in nature, with high emissions events coinciding with periods of high acceleration and speed. This research represents an attempt to bridge the gap in transportation and emission models, through the use of real-world distributions of Vehicle Specific Power (VSP) bins that are associated with average link speeds for various road classes. A successful effort in this direction would extend the use of transportation models to improve emissions estimation using the limited output produced by such models. In addition, the variability of emissions and emission rates over average speeds for a given facility type is explored and recommendations are made to extend the methodology to additional facility types.