Abstract-Many vehicle emission models are overly simple, such as the speed dependent models used widely, and other models are sufficiently complicated as to require excessive inputs and calculations, which can slow down computational time. We develop and implement an instantaneous statistical model of emissions (CO 2 , CO, HC, and NOx) and fuel consumption for light-duty vehicles, which is simplified from the physical loadbased approaches that are gaining in popularity. The model is calibrated for a set of vehicles driven on standard as well as aggressive driving cycles. The model is validated on another driving cycle in order to test its estimation capabilities. The preliminary results indicate that the model gives reasonable results compared to actual measurements as well as to results obtained with CMEM, a well-known load-based emission model. Furthermore, the results indicate that the model runs fast and is relatively simple to calibrate. The model presented can be integrated with a variety of traffic models to predict the spatial and temporal distribution of traffic emissions and assess the impact of ITS traffic management strategies on travel times, emissions, and fuel consumption.Index Terms-Instantaneous emissions modeling, integration of dynamic traffic and emission models, vehicle emissions and fuel consumption.

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Understanding the variations in travel by time of day is essential to predicting transportation system performance and air quality impacts of the transportation sector. As tour- and activity-based modeling procedures become more commonplace, the need for accurate time-of-day modeling procedures that are sensitive to changes in policies or travel conditions, such as congestion, that affect time-of-day choices, is clear. FHWA recently conducted a research project to develop new methods of modeling travel by time of day that are sensitive to these concerns. One of the products of this project is a time-of-day choice modeling procedure designed to be applied within tour- or activity-based travel modeling processes. This procedure was designed to be compatible with most existing tour- and activity-based models in the United States. The time-of-day choice model is estimated by using household activity survey data and transportation level-of-service information from the highway network. This procedure was tested by using the activity-based travel model for San Francisco County, California. The time-of-day modeling procedure is described, including the model estimation process, data requirements for estimation and application, and the results of the San Francisco test application. The test application included alternative scenarios designed to validate the model's sensitivity to land use, transit level of service, traffic congestion, and time-of-day pricing.

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