# Determining the Safety Level of State Roads: An Italian Case Study
## 1 Introduction  
Road traffic crashes (or accidents) are the eighth leading cause of death worldwide and the leading cause of death among children and young adults (aged 5-29 years) [1]. The European Union has set a goal of \"Vision Zero\" to eliminate all road traffic fatalities. To achieve this goal, the target for the 10-year period between 2020 and 2030 is to reduce the number of road deaths and serious injuries by 50% [2]. Similarly, Italy has set a crash reduction objective in line with the EU target [3]. However, Italian roads are still far from achieving the desired goal. In fact, according to the Italian Institute of Statistics, when comparing 2022 with the previous year, there is an increasing trend in road accidents (+7.2%) and road fatalities (+12.2%) on rural roads [4]. Moreover, comparing 2022 with the pre-pandemic situation, a slightly decreasing trend in road fatalities is recorded (3173 road fatalities in 2019 versus 3159 in 2022). Road managers have the duty to carry out numerous activities to improve the level of road safety. In Italy, some guidelines for road management activities have been published [5]. At the international level, other approaches are available, such as the one proposed in the Highway Safety Manual [6]. To manage an extensive road network, the first crucial step is to identify the most dangerous road sections so that a more detailed inspection can be planned. In fact, due to the vast scale of the national road network, it would be impossible to intervene simultaneously on the entire infrastructure, but some degree of priority should be assigned to different road sections. To assign a gradual level of priority to different road sections, the road network should first be divided into elementary sections of constant length to be analyzed. Then, each section should be evaluated in terms of safety level by adopting safety performance indicators. These indicators can quantify the actual level of safety by referring to different aspects. In fact, there are several safety performance indicators that can be taken into account, depending on the data available on the road network. In general, it is always preferable to consider more than one safety indicator at a time. Once safety performance indicators are associated with constant-length segments, these segments can be ordered from the most dangerous to the least so that field inspections can be planned accordingly. Italian guidelines [5] for road safety management usually refer to safety performance indicators based on the actual crashes that have occurred on the road in question. However, observed crashes are affected by the phenomenon of regression to the mean, meaning the fluctuation of the number of crashes around the average value. This is because crashes are rare, random, and independent events that should be carefully evaluated using statistical tools. The Italian reference also introduces the concept of Safety Potential (SAPO), which is the potential economic benefit that could be achieved on a road section thanks to the reduction of crashes by adopting idoneous measures. The SAPO is calculated based on the number of fatalities and injuries, the associated costs, and the risk exposure, which is evaluated by the Annual Average Daily Traffic (_AADT_). SAPO also depends on the base value of accident cost density, which is defined by the Italian guidelines developed in 2012 [5] and may need to be updated. However, SAPO is quite effective in providing an immediate result in terms of the road sections that should be urgently inspected. To overcome problems related to the random nature of crashes, the empirical Bayesian (EB) approach, based on predictive methods and observed crashes, can be adopted. These methods are usually an alternative to a reactive or preventive approach to road safety.