No abstract

The research aims to explore the effects of geometric road features on driver speed behaviour in order to identify unsafe road segments where high reductions in speed between successive road elements occur. The sample involves two-lane rural roads on flat terrain (vertical grade less than 5%) in Southern Italy, totalling 184 km without spiral transition curves between the tangent segments and circular elements. The testing was carried out on 567 study sites, of which 248 are on circular curves and 319 on tangents. Speed data collection was carried out in environmental and traffic conditions using a laser. The conditions were the following: dry roads, free flow conditions, daylight hours and good weather conditions. The main goal was to calibrate and validate different operating speed prediction models: a) one model on tangent segments; b) one model on circular curves; c) only one model to be used at the same time on tangents and circular curves. The validation process involved almost 10% of the total road network length, that was removed from the calibration phase. The speed measurements of each of the first two datasets (a, b) were grouped into ten homogeneous substrates while for the remaining dataset (c) sixteen substrates were defined by using a hard c-means algorithm. Two statistical criteria were used to remove anomalous operating speed values from each group of three datasets, namely, the Chauvenet criterion and the Vivatrat method. The first criterion was preferred in the final process of model selection. The results of the first filtering procedure showed more homogeneous samples that guaranteed a higher correlation coefficient and lower residuals of the predictive models during the validation phase than the Vivatrat method. The models were developed using an Ordinary Least Squares (OLS) method. The explanatory variables were total segment length, lane width, curvature of the road element, the curvature change rate on homogeneous road segments, and the number of residential driveways per km. ANOVA and additional synthetic statistical parameters were assessed to check the effectiveness of using a single general model to predict operating speeds at the same time on tangents and on circular curves alike. The results suggested the reliability of this hypothesis and its effectiveness in bringing advantages during the application phase.

Road safety has become a priority field worldwide and one of the major factors describing the state of the transport system with its positive and negative changes. Many studies on driver speed behavior can be found in the scientific literature, and researchers have addressed roadway alignment consistency for travel safety in the context of real operating speeds. This study illustrates an experimental analysis conducted on the Tirrenia Inferiore State Highway in southern Italy without spiral transition curves between geometric tangent and circular elements on the horizontal alignment in order to check a new prediction consistency model. Two consistency measures were developed and compared with the results available in the literature: the first was the relative area bounded by the speed profile and the average weighted speed, and the second was the standard deviation of operating speeds in each design element along the entire road examined. With a combination of these two previous measures and according to an extensive sensitivity analysis, a consistency model was developed and thresholds for good, acceptable, and poor road consistency can now be proposed. The consistency prediction model was related to the number of crashes occurring between 2003 and 2010. It was found that as design consistency increased, the number of crashes decreased significantly. The consistency model can be used for this purpose during the geometric design process or during the evaluation process for two-lane rural highways

One of the major tasks in developing transport systems is to decrease human losses caused by traffic accidents. The social consequences of accidents and the relating human losses were the main reason why the European Ministers of Transport decided to take measurements in 2002 and then in 2010 in order to decrease the number of traffic accident related deaths in Member States Italian and Lithuanian researchers have developed national statistical methods to answer to European directives in their own country. The aim of this research study is to investigate the safety conditions of Italian and Lithuania two-lane rural roads in order to figure out why accidents occur and by what means they can be avoided. Current safety situation needs to be known for selecting locations to be treated as well as for evaluating the effects. In fact the deaths of persons and serious economic loss caused by road crashes demand a continuous attention in accordance with the rapid population growth and increasing economic activities that have resulted in many European cities. A study period of 5 years of the accident database was investigated in order to estimate the hazard conditions for each road segment by comparing the number of crashes over a specific roadway segment over a specific time period with statistically thresholds. In this way, by knowing critical road segments, it makes to define a consistent combination of interventions according also to the difference between design and operating speed value reducing accident frequency, its severity and social cost for the more frequently expected and dangerous accident scenario. Further investigations on accident types in defined most hazardous road segments, i.e. where calculated severe crash rate, must be analyzed and selected road safety measures for improving safety situation at a site.