## 4 Conclusions  
This paper describes a theoretical model that is capable of calculating complex load safety requirements, including the load per cylinder, oil pressures, and tipping angle. It considers the trailers' mechanical properties, the cargo's characteristics, road inclinations, and wind pressure. The hydraulic cylinder suspension has been discussed, as well as how the hydraulic groups are defined. The hydraulic cylinders' spatial position provided a base for calculation of the \"stability area\" and \"plane of stability\". The trailer's load has been described by use of this data. They include the dead weight, dynamic forces, and aerodynamic forces. The combined force and \"stability area\" determined the transportation model's stability and the resulting \"tipping angle\" or instability. Finally, the load for each cylinder, load on each suspension group, and oil pressures have been calculated. The theoretical model that is proposed has been validated experimentally to measure oil pressures and the platform inclination. The MAPE of the oil pressures that were determined by the model is 7.0% for the data that were obtained experimentally. This error is minimal, which shows the validity of the proposed model. Once the proposed model was validated, an optimization algorithm was proposed in order to find the optimal center of gravity of the load, number of trailers, number of axles, oil pressures, and hydraulic configuration. The algorithm was based on the iterative and automatic testing of the proposed model in different positions on the trailer and different hydraulic configurations. The results showed that the proposed model and optimization algorithm can safely optimize the configuration of the hydraulic suspension of modular trailers in special road transport, increase the accuracy and reliability of the calculation of the load configuration, save time, simplify the calculation process, and be easily implemented. In summary, the novel theoretical model and optimization algorithm that this paper describes improves the reliability and accuracy of heavy transport stability calculations, saves time, minimizes human error, and greatly facilitates the decision-making process.  
Formal analysis: R.E.-G. and R.L.-L.; investigation: R.E.-G., M.C.-B., and A.A.; methodology: R.E.-G. and F.S.-G.; software: R.E.-G.; supervision: R.L.-L. and A.A.; validation: R.L.-L. and R.E.-G. Results, analysis, and manuscript preparation: all authors. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
**Institutional Review Board Statement**: Not applicable.  
**Informed Consent Statement**: Not applicable.  
**Data Availability Statement**: Not applicable.  
**Acknowledgments**: This research was supported with a grant from the Knowledge Transfer Partnership program (KTP), which is funded by Innovate UK (Project Reference 509302). The project was undertaken jointly by Leeds Beckett University and Collett & Sons Ltd. The authors greatly appreciate the invaluable help and the very considerable knowledge provided by co-KTP supervisors [PERSON] (Collett & Sons Ltd.), [PERSON], and especially [PERSON] (Leeds Beckett University) who sadly passed away during the project.  
**Conflicts of Interest**: The authors declare no conflict of interest.