New approaches for road safety assessment of vulnerable users

The increasingly frequent natural disasters, summed to the pandemic event, have leaded countries to reorganize their cities, habits, moves. The first step was to implement solutions to limit urban congestion by inducing citizens to prefer more sustainable and active ways. To discourage the use of motorized transport, more and more routes or areas for active users, as pedestrian or cyclists, should be dedicated. In order to conceive a safe and comfortable environment, specific studies and high budget, are needed. Due to the current economical constraints and the increasing need of physical distancing due to the pandemic situation, private and public road managers need procedures that maximize the resources to implement effective and sustainable interventions. It must be said that all the measures and actions implemented so far in the road sector are aimed at reducing the danger of the motorized component, but little has been done for vulnerable users. Unfortunately, in Italy there are still few regulations that can support technicians in the decision-making process. The most common way to solve the safety problem is the use of a systemic approach and this PhD thesis has the main objective of presenting a preliminary methodology for assessing the safety of vulnerable road users. In particular, the framework of the proposed procedure accompanies the sequence of the Chapters, which can be summarized as follows: • Introduction: this chapter presents the need to convert citizens' habits towards sustainability in order to respond to European demands. This requires the evaluation of road safety which can be pursued with different methods proposed in the literature; the one chosen in this study is based on risk analysis. • Chapter 1: deals with risk-based engineering analyzes, created mainly to activate forecasting and prevention measures in response to the damage generated by natural disasters. This made it possible to obtain a general definition of risk which was then extended to many other sectors such as the road sector. Then the different risk factors were identified (then examined in detail in the following chapters). • Chapter 2: notes the relationship between road safety and vehicle speed. a predictive model was developed to estimate the average speed of vehicles (which represents the vehicle exposure factor) as a function of the urban, rural and “transition” environment. This model starts from a recalibration and re-adaptation of the literature models using Floating Car Data (FCD). • Chapter 3: to assess the risk to which users are subjected in a road section, it is necessary to know not only the anthropometric data of the average user but also the exposure of vulnerable users, therefore the pedestrian and cycle flow. To estimate these flows, a hybrid methodology was defined which blends the purely configurational approach with the characteristics of the examination area and a demand-driven methodology. • Chapter 4: to prevent accidents at a site and predict the related consequences, since the data is not always available, a methodology has been proposed that enriches the existing vulnerability functions with the kinematic parameters of multibody simulations. • Chapter 5: once the risk factors were defined, a synthetic index was created. The latter allows to identify and classify the sites providing prioritization of interventions. To choose the type of countermeasure to be implemented, it is necessary to take into account the characteristics of the road, flows, speeds, the surrounding space, the hierarchy of the roads but also the available economic resources. Then, the most common countermeasures for the safety of pedestrians and cyclists were identified, their estimated average costs were considered and decision-making matrices of choice were proposed. This should allow the designer to have a procedure that, starting from the context and the risk factor, identifies the most convenient and effective countermeasure. • Chapter 6: among the many countermeasures, the one most used in urban areas to reduce the speed of vehicles is traffic calming. In this chapter, attention was focused on altimetric devices, analyzing the effects they produce on the human body (whether used temporarily or permanently, single or in series) using simplified models.