Validation Procedure for Predictive Functions of Driver Behaviour on Two-Lane Rural Roads

The study presented here aims to validate some operating speed prediction models calibrated on two-lane rural roads by using speed data collected in Northern and Southern Italy. Operating speed is defined as the speed at which drivers of passenger cars travel on a dry road in free flow conditions during daylight hours and it is calculated using a specific percentile of speed distribution, typically the 85th. Speed measurements were carried out by using laser detectors in connection with previous environmental and traffic conditions. The study is addressed to emphasize the reliability and easy application of one predictive speed model working both on tangent segments and on circular curves. The calibration phase involved roads in the Northern Italy, while the validation phase involved roads in the Southern Italy. Three models were validated applying them on eight two-lane rural roads falling within the road network of the Province of Salerno with features that reflect those adopted in the calibration phase; the selected models to be validated present the simplest analytical structure for type and number of explanatory variables and for the performance diagram shape of the operating speed values. The validation procedure was to estimate some synthetic statistical parameters as mean absolute deviation, mean squared error and coefficient of variation. The results allow in a simple way to trace continuous operating speed profiles on two-lane rural roads and to carry out safety analyses on the horizontal alignment

Motorway Speed Management in Southern Italy

AbstractComparing operating speed (V85) with the theoretical design speeds makes many of the assessments fundamental to correct design more effective. In technical literature various models for estimatingV85 are present but they cannot be extended to motorways without risking substantial approximation. This study proposes a model for estimating V85 on motorways. In addition, it proposes a second model making it possible to estimate free flow speed (FFS) in various traffic conditions. This could be very useful for Level of Service studies on motorways

BIM-LCA Integration Framework for Sustainable Road Pavement Maintenance Practices

The latest advancements in road asphalt materials and construction technologies have increased the difficulty for engineers to select the appropriate pavement design solution with consideration of life cycle assessment (LCA) methodology. On the other hand, infrastructure building information modeling (BIM) tools allow practitioners to efficiently store and manage large amounts of data, supporting decision making in road asphalt pavement design and management. This research contributes to setting up a dynamic LCA tool for the specific evaluation of designed road asphalt pavement solutions involving alternative materials and advanced recycling technologies; the tool is structured to minimize the need of input data by the designer, that are usually unknown during the early design stage, and automate the entire LCA calculation process to reduce the designer efforts and avoid any errors during data transcription. A traditional BIM workflow was integrated with additional user-defined property sets to simultaneously compute the environmental impact of the entire life cycle of the asphalt pavement, and dynamically update the result basing on the design thickness of the pavement layers, the specific features of materials and an external database of several life cycle impact category indicators that can be edited and updated gradually during more advanced design stage. The proposed BIM-LCA aims to be a practical and dynamic way to integrate environmental considerations into road pavement design, encouraging the use of digital tools in road industry and ultimately supporting a pavement maintenance decision-making process oriented toward circular economy

Freeway safety management: case studies in Italy

Road safety has since become one of the major factors for a description of the state traffic system and crashes are often due to bad made decisions by drivers in environments created by engineers. This study proposes an update of the previous version (Dell'Acqua et al. 2011a) to estimate V 85, for non-conditioned traffic flows on freeways. The databases used in the study come from a series of speed measurements and vehicle ranges on a stretch of freeway using a fixed measuring system. The produced model proved to be very reliable, with the greatest error in the estimation of V 85, being less than 6%. The model obtained was then applied to a stretch of freeway of approximately 20 km. Some significant correlations between DV 85 (variation of V 85 among successive stretches) and DN (the variation in the number of crashes among successive stretches) were found, which may be very useful in the management of safety on roads. In particular the obtained results have highlighted some aspects of motorway traffic. In addition, using the procedure illustrated, it has been possible to identify some particular ‘black spots’ due to the poor design co-ordination of the alignment, positioned between consecutive stretches (for approximately 2 km), with a difference in terms of V 85average greater than 10 km/h. First Published Online: 19 Sep 201

Safety performance functions for crash severity on undivided rural roads

tThe objective of this paper is to explore the effect of the road features of two-lane rural road networkson crash severity. One of the main goals is to calibrate Safety Performance Functions (SPFs) that canpredict the frequency per year of injuries and fatalities on homogeneous road segments. It was foundthat on more than 2000 km of study-road network that annual average daily traffic, lane width, curvaturechange rate, length, and vertical grade are important variables in explaining the severity of crashes. Acrash database covering a 5-year period was examined to achieve the goals (1295 injurious crashes thatincluded 2089 injuries and 235 fatalities). A total of 1000 km were used to calibrate SPFs and the remaining1000 km reflecting the traffic, geometric, functional features of the preceding one were used to validatetheir effectiveness. A negative binomial regression model was used. Reflecting the crash configurationsof the dataset and maximizing the validation outcomes, four main sets of SPFs were developed as follows:(a) one equation to predict only injury frequency per year for the subset where only non-fatal injuriesoccurred, (b) two different equations to predict injury frequency and fatality frequency per year per sub-set where at least one fa tality occurred together with one injury, and (c) only one equation to predict thetotal frequency per year of total casualties correlating accurate percentages to obtain the final expectedfrequency of injuries and fatalities per year on homogeneous road segments. Residual analysis confirmsthe effectiveness of the SPFs

Consistent Approach to Predictive Modeling and Countermeasure Determination by Crash Type for Low-Volume Roads

The object of this research is to develop one and only injury crash rate prediction model differentiable for three main crash types (head-on/side collisions, rear-end collisions, single-vehicle run-off-road crashes) observed on the selected Italian two-lane rural roads in low-volume conditions. An explanatory variable reflecting road “Surface” conditions (dry/wet), “Light” conditions (day/night), and geometric “Element” (tangent segment/circular curve) when the crash happened and referred to the police reports has been proposed within the safety performance function all together (Surface, Light and Element) with three other significant variables (lane width, horizontal curvature indicator and mean speed) as consistent factors to predict crashes and their degree of seriousness for different kind of crashes. Among different statistical approaches introduced in the past few years to deal with the data and methodological issues associated with crash-frequency data, a generalized estimating equation has been implemented to take into account over-dispersion of the crash data, with a negative binomial distribution additional log linkage equation. Residual plots were combined with the validation procedure and other goodness-of-fit measurements to determine the reliability of the results. Potential countermeasures have been proposed for the critical crash types surveyed on the studied roads; these countermeasures have had positive effects on the road segments where the serious crash types have occurred over an eight-year period of analysis

Evaluation of Climatic Factors Based on the Mechanistic -Empirical Pavement Design Guide

In this paper procedure for evaluating the effects of climate on pavement performance in Italy is proposed. To characterize the Italian territory nine different simulated scenarios have been used. These scenarios were obtained by combining three different situations of latitude (North, Central and South) with three conditions of altitude (high, medium, low altitude). For each of these scenarios, some configurations, proposed by the Italian CNR road pavement design catalogue with medium and high traffic flow, were verified using the Mechanistic-Empirical Pavement Design Guide. The results obtained showed that the Italian CNR road pavement design catalogue has a limited reliability