## 1 Introduction  
In recent years, high-speed rail express delivery, as an emerging mode of logistics transportation, has gradually entered the public's view. Railway transportation, while effectively meeting both passenger and freight demands, can also alleviate issues such as traffic congestion, energy shortages, safety concerns, and climate warming due to its high capacity, low energy consumption, low pollution, and high safety characteristics. There are three main reasons for the rapid development of high-speed rail express delivery: (1) the growing demand for logistics, coupled with a shift toward high-value-added products; (2) the continuous improvement in the high-speed rail network and ongoing innovations in high-speed rail technology; (3) compared to traditional road transportation, high-speed rail express delivery is more environmentally friendly, capable of reducing pollutant emissions and lowering carbon emissions.  
Scholars from various countries have long proposed different types of railway rapid freight products based on the operational status and speed attributes of each product, as shown in Figure 1.  
Even so, high-speed rail express delivery remains in its early stages compared to other transportation modes in the logistics industry and still faces numerous issues and challenges. With the continuously growing demand in the express delivery market, urgent questions include how to closely integrate high-speed rail with express delivery while maintaining passenger transport, and how to optimize the transportation capacity and utilization rate of high-speed rail express delivery.  
To address these issues, this paper examines the transport capacity of high-speed rail express delivery and passenger transport, revealing the impact of the high-speed rail express delivery model on passenger transport capacity. This study focuses on optimizingthe organization of high-speed rail express delivery to provide theoretical and methodological support for the rational development of high-speed rail express delivery. The main contributions of this paper include the following:  
1. Fully utilizing the advantages of high-speed rail to diversify the development of express delivery transportation.
2. Rational allocation of the remaining capacity of high-speed railways to enhance resource utilization.
3. Effectively controlling the impact of high-speed rail express delivery on passenger transport and coordinating the allocation of passenger and freight resources on high-speed rail lines.
4. Increasing the market share of railway express delivery, reducing costs, and increasing the revenue of railway transport enterprises.  
The remainder of this paper is organized as follows: Section 2 provides a literature review on the current status of high-speed rail express feasibility and optimization of high-speed rail express. Section 3 proposes the non-splittable high-speed rail express transportation scheme model. Section 4 presents a case study that demonstrates that the model is computationally tractable and practicable under different scenarios, and gives the transportation plans. Section 5 concludes the paper and presents future research directions. Section 6 provides a thorough discussion on the results.