## 3 Experimental Results and Analysis
### Comprehensive Analysis of Factors Influencing Climbing Characteristics  
During the uphill journey, the speed of heavy-duty vehicles tends to decrease to varying degrees, causing disturbance to trailing vehicles and potentially leading to severe  
Figure 9: The speed of heavy-duty vehicles on roads with a design speed of 120 km/h. (**a**) Traditional fuel-powered heavy-duty vehicles; (**b**) pure electric heavy-duty vehicles. -rear-end accidents [34]. Hence, it is customary to regulate the minimum travel speed on inclines to ensure road traffic safety and enhance highway capacity and service levels. Based on the definition of vehicle speed coordination in the \"Highway Project Safety Evaluation Code\" (JTG B05-2015), this paper introduces the climbing speed decay degree (\(DV\)) to precisely analyze the influencing factors of uphill characteristics for pure electric heavy-duty vehicles. This index not only characterizes the degree of speed variation during uphill travel but also reflects the magnitude of speed changes throughout the uphill process, thereby restraining the minimum travel speed on inclines. The formula for this index is as follows:  
\[DV=\left|\frac{v_{1}-v_{2}}{v_{1}}\right| \tag{5}\]  
In the equation, \(v_{1}\) represents the maximum driving speed of vehicles on vertical curves and uphill sections, while \(v_{2}\) denotes the minimum t driving speed of vehicles on uphill sections. Existing studies have predominantly focused on the uphill speed characteristics of heavy-duty vehicles, primarily traditional fuel-powered ones, from a single-factor perspective. These studies typically examine the individual impacts of factors such as slope, slope length, load weight, specific power, and initial climbing speed on the variation in vehicle climbing speed. However, in actual uphill scenarios, the speed variation of vehicles is influenced by multiple factors simultaneously. Therefore, this study investigates the speed variation characteristics of pure electric heavy-duty vehicles under the joint influence of multiple factors. Utilizing simulation-derived data, interpolation methods are applied in MATLAB(R2018a) software to process the data and generate three-dimensional visualizations, as depicted in the following figure, to more accurately and vividly depict the variation pattern of vehicle climbing speed under the combined effects of multiple factors. Existing research primarily focuses on traditional fuel-powered heavy-duty vehicles from the perspective of single factors, analyzing the impact of individual factors, such as grade, slope length, load weight, power-to-weight ratio, and initial climbing speed, on vehicle climbing speed changes [3; 5; 7]. However, in actual climbing processes, the change in vehicle climbing speed is influenced by multiple factors collectively. Therefore, this paper investigates the characteristics of climbing speed changes in pure electric heavy-duty vehicles under the combined influence of multiple factors. Based on simulation data, interpolation methods are employed to process the data using MATLAB software. The climbing speed decay degree (\(DV\)) is introduced to represent the speed loss during vehicle climbing, resulting in a three-dimensional graph as shown below, which more accurately and vividly reflects the pattern of vehicle climbing speed changes under the combined effect of multiple factors. Based on the analysis above, it is evident that when the longitudinal slope gradient is steep, pure electric heavy-duty vehicles attain their highest speeds on gradual vertical curve sections and reach their lowest speeds on straight longitudinal slope sections during uphill climbing. Analyzing the influencing factors of climbing speed for pure electric heavy-duty vehicles reveals that on the experimental route, the slope primarily affects the vehicle's minimum driving speed on straight uphill sections, while the initial climbing speed affects the vehicle's maximum speed on both straight and gradual vertical curve sections.