Dr. Francesco Viti

Delft University of Technology, NL

January 23, 2009, 09:15, Room GC C3 30 (click here for the map)

Driving Behavior and Emissions at Signals: a Microscopic Approach

Growing concerns over degrading air quality and climate change have led to the implementation of measures to reduce road traffic emissions, among them Intelligent Transport Systems (ITS). Such measures influence traffic flows in many, often subtle ways. The assessment of these measures is not straightforward as the effects are often found on the microscopic level, i.e. the movement of individual vehicles, and are difficult to observe directly. However, as ITS measures become more common, and environmental aspects more important, there is a need for reliable tools to evaluate the effects of ITS measures on emissions. Several traffic and emission models are available; the question is whether they can model accurately enough both the traffic and the produced emissions. Microscopic simulation programs are often used in practice for assessing the effects of ITS strategies, since they enable one to calculate the trajectory and the characteristics of each vehicle and of the network under different scenarios and road conditions, and to model vehicles' and drivers' behavior with enhanced detail and at fractions of a second. However, in these models, measures like speed, acceleration and deceleration are still determined by a limited set of parameters, which are rarely chosen based on field measurements. One main reason is that collecting real vehicle trajectories, able to quantify and explain these parameters, is a very challenging task. At signalized intersections more difficulties arise, since traffic flows are interrupted by the traffic control signal, and driving behavior strongly depends on the current state of the system, i.e. whether drivers have right of way, or they have to stop in queue etc. We propose a method to collect such dataset using image processing techniques, which allows one to obtain a full vision on the traffic process at the signal, and to measure individual vehicle speeds and accelerations at a microscopic level. By using microscopic trajectory data we can gain insight into the behavior of drivers, i.e. the way they approach the signal and interact with the traffic control and the other vehicles. Therefore, analysis of real driving behavior from a microscopic scale enables us to evaluate the speed and acceleration behavior at these systems under different traffic conditions, and to quantify the differences observed in the (longitudinal) driving behavior within these systems, e.g., in terms of interdriver heterogeneity as well as intradriving variability and with different traffic and control states. Using this unique dataset, direct calibration of the main parameters in two widely used commercial microscopic software programs, VISSIM and AIMSUN, could be performed, and validation and comparison could be operated in terms of individual speeds, speed variations and for the estimation of emissions concentrations. As a result of this analysis, we highlight a number of inconsistencies between simulation and reality, due to simplifications in driver's free driving as well as in car-following mode. Lacks in intradriving variability and anticipatory behavior in these programs suggest that they may not provide realistic results for these types of road sections, even when carefully calibrated.


Francesco Viti was born in Matera (Italy) in 1975. He graduated "Summa Cum Laude" in Civil Engineering, majoring in Transportation Engineering, at the University "Federico II" of Napoli in 1994. In his final M.Sc. thesis he developed a framework for the optimization of urban accessibility using a Park Pricing strategy. In 2001 he joined the Dynamic Traffic Management group of the Delft University of Technology, starting a Ph.D. research which ended in 2006 with the writing of a dissertation entitled "The Dynamics and the Uncertainty of Delays at Signals". During this period he produced a number of high impact articles and presented his work at many international conferences. He was awarded in 2004 with the prize "Best Paper for a Young Researcher" the 10th WCTR Conference in Istanbul. He is currently employed at both Delft University of Technology and at the Katholieke Universiteit Leuven since January 2007, participating actively on research projects on different areas, e.g., ADAS systems, ICT technologies, advanced data collection systems, incident analysis, emission modeling, travel time prediction, real-time dynamic traffic management, traffic flow theory and simulation. During this period he was involved in various projects and teaching activities. He was course leader of "Game Theory: theory and applications in transportation" given at the TRAIL Research School and lecturer of the TU Delft course "Data Collection Methods and Analysis". Moreover he gave his contribution to doctoral and project researches on travel information systems, pricing, travel time prediction, Advanced Driver Assistance Systems etc. He is involved in the evaluation of European Commission projects for both FWP6-INFSO e FWP7-ICT, and reviewer for high impact journals.