# A Survey on Variable Neighborhood Search for Sustainable Logistics
## 4 Results and Findings
### Sustainability Analysis
#### 4.5.2 Environmental Criteria  
In the context of the use of VNS for sustainable logistics, we have identified several key environmental aspects that are commonly addressed in research. We have further categorized each paper based on these specific aspects. To facilitate this, we considered 11 distinct fields:  
* Electric vehicles: This category includes papers that explore the use of electric vehicles (EVs), which are pivotal in reducing the environmental impact of logistics by minimizing reliance on fossil fuels.
* Emissions: Papers in this group focus on strategies to minimize emissions, such as carbon dioxide, nitrogen oxides, and particulate matter, from transportation and logistics operations, highlighting the importance of cleaner and greener practices.
* Waste collection: This category encompasses studies dedicated to optimizing waste collection systems, improving efficiency while ensuring sustainable waste management practices.
* Energy consumption: Papers classified here address the reduction in energy consumption within logistics operations. Some of these studies involve mixed fleets that combine traditional and alternative energy sources, with a focus on improving overall energy efficiency.
* Drones: This field includes research that explores the use of electric drones for logistics, which offers the potential for lower emissions and greater efficiency in last-mile delivery, particularly in urban or remote areas.
* Reverse logistics: Papers in this category focus on reverse logistics processes, which involve the return of goods from consumers to producers, and emphasize sustainable practices such as recycling and reusing products.
* Closed-loop logistics: This category includes studies that look into closed-loop logistics systems, which are designed to ensure products are reused or recycled, minimizing waste and reducing the need for raw materials.
* Clean energies: This field encompasses papers exploring the use of clean energy sources such as wind farms, biomass energy, and photovoltaic (solar) energy within logistics, aiming to reduce the environmental footprint of operations.
* Sustainable Tourism: Studies in this category focus on the intersection of logistics and sustainable tourism, addressing how transportation and logistics systems can support environmentally responsible travel practices.
* Noise pollution: This group includes papers that address the issue of noise pollution, which is an often-overlooked aspect of sustainability in logistics, focusing on strategies to reduce noise emissions from transportation vehicles and operations.  
* Wastewater collection: Finally, papers related to wastewater collection explore logistics systems that are designed to manage and transport wastewater in a sustainable manner, minimizing environmental impact and optimizing infrastructure.  
By organizing the papers into these 11 categories (see Table 11), we provide a clearer understanding of how environmental criteria are integrated into various logistics problems using the VNS and highlight the diverse ways in which environmental concerns are being addressed in the field. Figure 7 shows the distributions of papers according to these categories. Among these various fields, the use of electric vehicles and the reduction in carbon emissions are the most frequently considered in the literature. This reflects the growing global emphasis on decarbonizing the transportation sector and transitioning toward greener logistics practices.