## 4 Discussion and Conclusions
Therefore, future research will delve into longitudinal slope design suitable for the trends of electrification and intelligence, providing insights for future highway construction. The main contributions of this study are as follows:  
1. This study takes into account the climbing habits of drivers and highway route design to design an experimental road, which includes sections for linear acceleration energy storage, vertical curve sections with minimum length control, and longitudinal slope sections with varying gradients. 2. A co-simulation simulation platform for pure electric heavy-duty vehicles was constructed using TruckSim and MATLAB/Simulink;
3. Comparative research reveals that compared to traditional fuel-powered heavy-duty vehicles, pure electric heavy-duty vehicles demonstrate smoother acceleration and deceleration processes, smaller speed fluctuations, higher travel speeds, and greater equilibrium speed values during uphill climbing;
4. By introducing the climbing speed decay degree (\(DV\)), an analysis was conducted on the characteristics of speed variation in pure electric heavy-duty vehicles under the joint influence of multiple factors. It was found that the power-to-weight ratio has a greater impact on the climbing speed of pure electric heavy-duty vehicles compared to initial vehicle speed, which only affects the vehicle's maximum travel speed;
5. Based on the minimum speed requirements for uphill travel specified in the \"Specification\" and considering the equilibrium speeds of pure electric heavy-duty vehicles under different longitudinal slope conditions, the maximum grade suitable for the dynamic performance of pure electric heavy-duty vehicles was derived. However, it was observed that the dynamic performance of pure electric heavy-duty vehicles does not align with the maximum grade stipulated by the \"Specification\";
6. The introduced \(DV\) is intended to reflect the perceptual differences of drivers when heavy-duty vehicles climb slopes at different design speeds. Using \(DV\) as a control metric, the critical length for the safe operation of pure electric heavy-duty vehicles was determined. Conceptualization, Y.P. and L.H. ; methodology, L.H. ; software, S.P. ; validation, L.H., S.P. and Y.W. ; formal analysis, Y.P. ; investigation, L.H. ; resources, L.H. ; data curation, S.P. ; writing--original draft preparation, L.H. ; writing--review and editing, Y.P. ; visualization, S.P. ; supervision, Y.P. ; project administration, Y.W. ; funding acquisition, Y.P. All authors have read and agreed to the published version of the manuscript. This work was supported by the National Natural Science Foundation of China [grant number 51278158]. **Informed Consent Statement:** Not applicable. **Data Availability Statement:** The data that support the findings of this study are available from the corresponding author upon reasonable request. **Conflicts of Interest:** The authors declare that there are no conflicts of interest regarding the publication of this article. There are also no conflicts of interest between the authors and the co-authors. The submitting authors are responsible for co-authors declaring their interests.