## 2 Literature Review
### Application of Life Cycle Sustainability Assessment (LCSA) in Bridge Projects  
The United Nations Environment Program (UNEP) defines sustainability as a global goal comprising environmental, economic, and social dimensions. The growing emphasis on sustainability has led to the development of the Life Cycle Sustainability Assessment (LCSA), a comprehensive approach that evaluates the full range of environmental, social, and economic impacts of products. Introduced over 15 years ago, LCSA integrates Environmental Life Cycle Assessment (E-LCA), Life Cycle Costing (LCC), and Social Life Cycle Assessment (S-LCA) based on standards like ISO 14044, ISO 14040, ISO 14047-ISO 14049, ISO 15663, and ISO 14072. Aligning with triple-bottom-line theory, LCSA supports sustainable decision-making across a product's life cycle. [PERSON] first presented the term \"LCSA\" in 2007 and [PERSON] further developed it in 2008, marking a significant advancement in sustainability assessment [7; 78; 79; 80; 81; 82; 83]. The field of LCSA is continually evolving, with ongoing efforts to refine its framework and methods to more accurately measure sustainability. LCSA's broad applicability spans industries such as construction, transportation, manufacturing, energy, and agriculture, aiming to promote a Circular Economy (CE), which emphasizes sharing, reusing, repairing, and recycling resources to reduce greenhouse gas emissions and extend material lifespans. Life Cycle Assessment (LCA) assesses environmental impacts within specific system boundaries, while Life Cycle Costing (LCC) addresses economic aspects, ensuring accurate cost planning throughout a product's lifecycle. The addition of the Social Life Cycle Assessment (S-LCA) broadens LCSA by evaluating the social impacts on stakeholders at various levels. While LCSA still requires further development to enhance its applicability, it plays a critical role in advancing a sustainable economy by integrating sustainability with economic and social considerations, aiding informed decision-making in design and construction projects [7; 82; 83; 84; 85; 86; 87; 88; 89; 90]. In bridge projects, LCSA has evolved from managing material life cycles to analyzing environmental impacts and maintenance challenges. Initially, LCSA focused on comparing the lifespans of standard and minimal-girder bridges through steel durability tests to enhance performance. Further developments included evaluating conventional versus alternative materials for bridge decks to extend their lifespan and reduce maintenance needs [34,60]. The scope of LCSA has expanded to evaluate the environmental impacts of railway bridge construction, highlighting the significant effects of material production. Comprehensive assessments have measured the environmental impacts of various bridge activities and components using diverse environmental indicators. Studies on completed bridges have shown that material manufacturing and operation stages are major contributors to environmental impacts. Exercise-based Life Cycle Assessment has provided insights into the environmental sustainability of bridges, especially in critical stages like raw material manufacturing and processing [18,36,37,38]. Regular bridge maintenance is critical for reducing costs and minimizing environmental impacts, compared to the higher investments and environmental consequences of irregular maintenance. In bridge projects, LCSA encompasses material management, environmental impact analysis, and maintenance considerations to promote sustainable infrastructure development [39]. Several studies have combined Life Cycle Assessment (LCA) and Life Cycle Costing (LCC) to better manage environmental impacts and costs in bridge maintenance. A genetic algorithm-based framework was developed to optimize bridge maintenance, focusing on maximizing safety, minimizing costs, and reducing environmental effects.