Lane-Distribution Models and Related Effects on the Capacity for a Three-Lane Freeway Section: Case Study in Italy

Abstract

Traffic flow, its characteristics, and road quality service are usually estimated by using aggregated and averaged data from multiple lanes; however, in real experiences, there is significant variability in traffic-flow parameters across the different freeway lanes. Among the numerous factors that affect traffic distribution are vehicular composition, driver behavior, regulations about passing and overtaking, lane discipline, and designated lanes. Because these factors are very specific, the models and values for traffic distribution in a multilane freeway segment are highly sensitive to their national context. This study starts from an analysis of the capacity of a three-lane test segment within the Italian freeway system, and then examines the manner in which the flow and density vary across the freeway lanes. The analysis is restricted to up-to-capacity conditions and nonlinear regression models of the distribution relationships are calibrated for each lane, for both flow and density ratios, as a function of the total flow. The nonhomogeneous use of freeway lanes in Italy can be qualified and quantified through the trends found in these ratios, and then compared with similar internationally focused studies. This provides a useful interpretation of driver behavior, and is also a reference for calibrating traffic models, supporting design and operational processes and the implementation of intelligent transportation systems (ITSs) that are consistent with the national context.