PSI - Issue 62

Giada Limongi et al. / Procedia Structural Integrity 62 (2024) 97–104 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

98

2

Keywords: Bridge risk assessment, risk exposure, territorial accessibility, inner areas.

1. Introduction The accessibility of territories basically depends on the functionality and redundancy of the road infrastructures and their critical elements like bridges (Buratti et al. 2021). The road network serves as main link for accessing essential services, economic development, and strengthen social connection. In peripheral areas, the accessibility to essential services is one of the main features to determine the local resilience (Compagnucci, Morettini 2020) threatened by their progressive marginalization due to shrinking socio-economic processes (Vitale Bovarone, Cotella 2020). However, the reliability of road network is increasingly challenged by multifaceted natural hazards, including the growing climate-related events (Martin et al. 2021), as well as the aging of infrastructure and the lack of maintenance. Geological events, such as landslides, floods, earthquakes, wildfires can damage critical elements such as bridges and make territories already characterized by poor accessibility temporarily inaccessible. Also, the growing extreme hydrometeorological events, such as heavy rainfalls or floods, can cause damage and deterioration of roads and their critical elements. This last aspect, together with the ageing of many road infrastructures built in the last Century, makes adaptive strategies essential to increase the resilience of the road network and ensure the accessibility of territories both for accessing essential services, economic development, social connection as well as for emergency response. Understanding the overall role of the road network allows to intertwine the detailed analyzes on the vulnerability of roads’ critical elements with territorial analyzes on accessibility of peripheral areas. The ministerial Guidelines for the risk assessment and management of existing bridges (Minister of Infrastructure 2020) provide a multi-level risk-based approach to support management and maintenance strategies tailored to the several features of each bridge (Di Sano et al. 2023). In particular, the ministerial Guidelines assume the strategic role of bridges and the entire road network as key parameters to evaluate the exposure level. The presence of road alternatives is one of the parameters for determining the exposure class of bridges. In case of bridges interruptions or traffic limitations, the guidelines suggest evaluating the presence of possible road alternatives and their adequacy in terms of costs, time, and distances. The absence of alternatives determines an increase in the exposure class of the bridge which acquires greater strategic relevance for the accessibility of the territory. Data and information to evaluate the presence and adequacy of the alternative can be deduced from specific transportation studies, if available. Otherwise, the guidelines suggest assuming the case of "absence of alternatives" as a precautionary condition and, therefore, increasing the exposure class. This contribution suggests a method to determine the presence of alternative roads based on travel times adopted by the national classification of inner areas. The proposal allows to relate the exposure class of the bridges to the degree of peripherality of the territories they connect, both to identify threshold values for the definition of the exposure levels of bridges and define priorities for intervention on them. The method is tested on a set of Municipalities characterized by a high degree of peripherality according to the national classification provided by the National Strategy for Inner Areas (SNAI) in order to focus on territories already characterized by lack of essential services, which therefore may suffer more from interruptions along the main roads. 2. Material and method In 2014, the National agency for territorial development launched the SNAI to counteract the demographic decline and ensure all citizens have full access to the essential rights (public transport, healthcare, education). To this aim, the Italian municipalities were classified according to their degree of peripherality by considering the distance of each municipality from the nearest service center (Department for Cohesion Policies 2020). The municipalities containing essential services are classified as Municipal (A) or Intermunicipal (B) centers. For all the other municipalities, the classification depends on the average road travel time to reach the nearest center as follow: • C - Belt municipalities, minimum road travel time 0 minutes;

• D - Intermediate municipalities, minimum road travel time 27,7 minutes; • E - Peripheral municipalities, minimum road travel time 40,9 minutes; • F - ultra-peripheral municipalities, minimum road travel time 66,9 minutes;