# Drive on a Greener Way: A Case Study on Navigating Cross-Regional Traffic Networks in South China
## 3 Sustainable Mobility Model
### Road Model Estimation  
The main sources of carbon emissions from traffic are vehicles and roads. According to the LCA, carbon emissions are not only generated by fuel consumption but also by the maintenance of vehicles and roads. In this method, the carbon emission calculation of sustainable mobility does not include the carbon emissions generated during the construction of cars and roads, because these carbon emissions are not generated by traffic. Therefore, the carbon emissions can be divided into the following five parts. * Carbon emissions from vehicle fuel consumption. Gasoline is a carbon-containing material that emits carbon dioxide when used. The factors influencing CO2 emissions can be divided into vehicle aspects, roads, and traffic states. Different types of cars have different levels of fuel consumption per kilometer, so their carbon emissions are different. An increase in the length of the road will increase the total fuel consumption. Traffic flow is also a key factor that affects the fuel consumption. If the traffic flow is too high, it will slow down the traffic speed and increase the fuel consumption, which will increase the carbon emissions. Rain is a negative factor associated with carbon consumption, because the vehicle needs more power to maintain its balance. Thus, the carbon emissions caused by vehicle fuel consumption can be expressed as Equation (1). \[E_{1}=f_{1}(fuel\_consumption,\,road\_length,\,congestion,\,weather) \tag{1}\]
* Carbon emissions from vehicle maintenance  
The CO2 generated by vehicle maintenance refers to the periodic maintenance carried out after the vehicle has travelled a certain distance. The Chinese government requires maintenance for vehicles traveling 5000 km. The vehicle maintenance process consumes carbon-containing substances such as oil as well as CO2. The consumption of carbon-containing substances is mainly directly related to the car type and fuel consumption: the higher the fuel consumption, the higher the maintenance consumption. Thus, the carbon emissions caused by vehicle maintenance, \(E_{2}\), can be expressed as Equation (2). \[E_{2}=f_{2}(car\_type,\,fuel\_consumption,\,road\_length) \tag{2}\]
* Carbon emissions from road maintenance  
Road maintenance involves the repair of damaged roads caused by vehicle traffic. During this process, materials such as asphalt and cement are used, along with large energy-consuming machinery that emits CO2. The carbon emissions generated from road maintenance are directly related to the materials used and the type of road. Different types of road surface and damage require different repair techniques and materials. Roads, bridges, and tunnels have different maintenance needs and consume different materials. The carbon emissions produced from road maintenance can be adjusted based on several factors, including the time taken for the servicing of roads, the annual rainfall, and the annual traffic flow. Heavy rainfall will increase the frequency and complexity of maintenance. High traffic flow can increase the damage level and lead to higher carbon emissions during periods of maintenance. The carbon emissions associated with road maintenance can be expressed using Equation (3):  
\[E_{3}=f_{3}(material,\,time\,in\,service,\,annual\_rainfall,annual\_ traffic\_flow) \tag{3}\]
* Carbon emissions from road maintenance patrols  
Patrol refers to the inspection of road damage. The method is driving on the road by professional staff for inspection. There is a positive correlation between patrol frequency and traffic flow. The carbon emissions generated in the process of road patrol are fuel consumption. Carbon emissions of road maintenance patrols can be expressed as Equation (4). \[E_{4}=f_{4}(patrol\_frequency,\,road\_length,\,annual\_traffic\_flow) \tag{4}\]  
\(\bullet\) Carbon emissions from additional road maintenance and road inspections  
In addition to periodic road maintenance, other factors can cause additional maintenance needs for roads.