# Evaluation of Turkey's Road-Based Greenhouse Gas Inventory and Future Projections
## 3 Results  
### Greenhouse Gas Emission Calculations from State Roads  
This study examined the emissions of direct GHGs, primarily CO\({}_{2}\) and N\({}_{2}\)O, and indirect GHGs, including NH\({}_{3}\), NO\({}_{\chi}\), SO\({}_{2}\), CO, NMVOC, and PM, all of which contribute to the indirect greenhouse effect. The calculations were performed for 11 years, from 2010 to 2020. The results obtained are given in Table 3.  
When the results of the study were evaluated (Table 3), the amounts of CO\({}_{2}\), N\({}_{2}\)O, NH\({}_{3}\), NO\({}_{\chi}\), SO\({}_{2}\), CO, NMVOC, and PM increased by 29.6%, 24.2%, 0.5%, 19.9%, 9.9%, 18.2%, 21.5%, and 39.7%, respectively, in 11 years. Of all the contaminants, the PM showed the highest increase of 39.7%, while the NH\({}_{3}\) showed the smallest increase of 0.5%. This situation relates to the types of fuel used by vehicles. An analysis of the fuel types of vehicles used in traffic reveals that diesel cars, LPG-fueled cars, LCVs, and HDVs have experienced growth rates of 3.60, 1.64, 2.06, and 1.15 times, respectively, over the past 11 years. In contrast, petrol cars have seen a decline of 0.82%. Diesel-fueled automobiles, LCVs, and HDVs collectively account for almost 50% of all vehicles on the road. Although diesel-powered cars produce more PM emissions than petrol-powered vehicles, petrol-powered vehicles emit more NH\({}_{3}\) emissions than diesel-powered vehicles [34]. Consequently, while the type and quantity of emissions vary depending on the fuel used, the dominance of oil as the primary fuel in the transportation sector is highly significant. A review of the literature reveals that the increases in traffic-related greenhouse gas emissions in Turkey and other nations are noteworthy [20; 24; 47; 48]. To mitigate the rise in GHG emissions, one practical approach is to impose restrictions on the use of fossil fuels. To achieve carbon neutrality across all sectors, including transportation, the European Union has declared its intention to prohibit the sale of diesel and petrol automobiles entirely by 2035 [49]. Nevertheless, the rate at which the automobile sector in Turkey is adapting to this transition is unclear. Anticipating its global ubiquity is an inaccurate perspective. Fluctuations and advances in the transportation industry are varied. It is recommended to use numerous preventive applications to provide higher precision in reaching the desired effect. Upon analyzing the calculated emission values, a consistent rise became evident between 2010 and 2018 (Table 3). However, between 2018 and 2020, the levels of CO\({}_{2}\), N\({}_{2}\)O, NH\({}_{3}\), NO\({}_{\chi}\), SO\({}_{2}\), CO, NMVOC, and PM decreased by 3.9%, 6.4%, 8%, 5.3%, 6.3%, 8.5%, 8.1%, and 4.4%, respectively. The decrease in the number of cars on the roadways covered in the research may be attributed to the impact of lockdown, which reduced vehicle traffic during the pandemic. Specifically, vehicles decreased from 19,379,148 in 2018 to 19,132,034 in 2019 and 17,917,138 in 2020. Schools, colleges, shops, restaurants, and gyms, where people congregate in large groups, were temporarily shut down due to restrictions. In addition to solutions to reduce the number of trips on public transportation, isolation measures were also implemented among the population. As a result of these measures, access to shops and transportation hubs was reduced by around 80%, and access to workplaces was decreased by about 45% [50; 51]. These applications indicate the cause of the decrease in car usage. Furthermore, the construction of highways, tunnels, and bridges to enhance the efficiency, cost-effectiveness, sustainability, and environmental friendliness of road transportation nationwide may also have a positive impact. The road network, which was 62,864 km in the early 2000s, has risen to 68,266 km in the 2020s, and the number of tunnels has increased from 83 to 488 [27]. Therefore, part of the reduction in emissions in these years can also be attributed to a decrease in the distances traveled.