Truck Modeling Along Grade Sections

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Virginia Tech

This research effort first characterizes the trucks traveling along US highways by analyzing data from Interstate 81. It is hypothesized that I-81 is typical of US highways and thus can provide some insight into typical truck characteristics. These truck characteristics are important for the development of an exhaustive vehicle performance procedure. Analysis was done based on data collected at the Troutville weigh station. The characterization involves an analysis of vehicle class distribution, GVW (Gross Vehicle Weight) distribution, vehicle volume distribution, Average Weight on Tractive Axle (AWTA), and typical weight-to-power ratios. The thesis then assembles a database of systematic field data that can be utilized for the validation of vehicle performance models. This database is unique because it was conducted in a controlled field environment where the vehicle is only constrained by its dynamics. Using the assembled field database, a simple constant power vehicle dynamics model for estimating maximum vehicle acceleration levels based on a vehicle's tractive effort and aerodynamic, rolling, and grade resistance forces was tested and validated. In addition, typical model input parameters for different vehicle, pavement, and tire characteristics are included in the thesis. The model was found to predict vehicle speeds at the conclusion of the travel along the section to within 5 km/h (3.1 mi/h) of field measurements, thus demonstrating the validity and applicability of the model. Finally, the research effort introduces the concept of variable power in order to enhance current state-of-the-art vehicle dynamics models and capture the build-up of power as a vehicle engages in gearshifts at low travel speeds. The proposed enhancement to the current state-of-practice vehicle dynamics model allows the model to reflect typical vehicle acceleration behavior more accurately. Subsequently, the model parameters are calibrated using field measurements along a test roadway facility.

Traffic flow theory, Truck modeling, Vehicle dynamics, Traffic modeling