# Research on Freight Transportation Carbon Emission Reduction Based on System Dynamics
## 1 Introduction
In natural sciences, the allocation of irrigation resources has also been resolved through system dynamics analysis [30]. System dynamics analysis methods are also widely used in the field of construction engineering and have been applied in the construction and demolition of old buildings [31; 32]. Some scholars have used system dynamics models to simulate energy policies and obtained positive feedbacks [33]. System dynamics is also widely used in power grid systems [34]. In the medical field, scholars also use the system dynamics model to study the sharing of medical information and the medical supply chain [35]. A toolkit of designs for mixing discrete event simulation and system dynamics has also been researched and published by scholars [36]. First, some scholars have discussed and studied how to implement carbon tax among the population and gain the public's support for carbon tax [37; 38]. Some organizations have analyzed the basis of the carbon tax [39]. Scholars in different fields have conducted research on the collection of carbon taxes from several aspects: the impact on social inequality and the impact on energy, the environment, and the economy [40; 41]. One paper  
Figure 1: Causality diagram. determines the specific value of carbon tax based on the impact of different carbon taxes on carbon emissions [42]. In the field of consumption, some scholars analyze the impact of carbon tax on consumers and retailers from the perspective of revenue sharing and cost sharing [43,44]. There have been many studies on the specific measures of carbon tax collection in recent years. For example, a paper has described research on supply chain network design under an uncertain carbon tax [45]. Research on the economic and environmental integrated model of the multi-stage cold supply chain is ongoing [46]. Scholars use data envelopment analysis to determine the optimal carbon tax rate [47]. Researchers have discussed the impact of carbon tax on industrial production plans under the Industry 4.0 system [48]. Some scholars have optimized the supply chain path selection under the condition of carbon tax [49]. An off-design model to optimize a combined cooling, heating, power, and ground source heat pump (CCHP-GSHP) system considering carbon tax is given [50]. Some scholars have conducted research on supply chain cost-sharing contracts in the context of the carbon tax and have also conducted relevant discussions on the trading of emission rights [51,52]. Spanish scholars discussed the effect of additional taxes on heavy goods vehicles, and the result showed that the additional taxes did not cause freight volume changes or a shift of freight to alternative modes [53]. Italian scholars conducted an economic analysis of the road-to-rail transition at the policy level, and calculated the economic benefits of the policy [54]. Carbon emissions have had a great impact on the global climate and environment. As one of the industries with the greatest carbon emissions, the main trend of the transportation industry will be reducing carbon emissions in the future. In order to coordinate and promote the adjustment of transportation structure, it is an important measure to transfer part of the road freight volume to railway freight. Based on the above background, this paper focuses on roads and railways in the transportation industry, starting from the demand for road-to-rail transportation, and discusses environmental protection investment and carbon tax to increase the demand for road-to-rail transportation. Since this research aims at reducing the impact of carbon dioxide emissions in the road and railway system, it could be a useful resource to assist the government in improving the guidance policy. As the research of road-to-rail transportation does not involve the well-to-tank process, this paper only discusses the tank-to-wheel process in transportation systems.