## 1 Introduction  
As freight volume increases due to globalization, real concerns about the environmental impact of freight transportation have arisen. Freight is transported via various modes, such as truck, rail, ship, or aviation. [1]. Each mode has different characteristics in terms of cost, transport time, and accessibility but all have in common that they emit greenhouse gases and pollute the environment. Freight transport is responsible for 14% of global greenhouse gas emissions [2, 3]. Looking at the forecast of greenhouse gas emissions based on the demand trend of cargo handling volume, they are expected to increase even more than the surveyed figures. As environmental issues related to greenhouse gas emissions have attracted attention, many countries and companies have attempted to find alternative transportation solutions to minimize those emissions [4, 5].  
One such alternative solution is intermodal freight transportation systems, which are defined as a method of transportation of loads from origin to destination employingat least two transport modes, such as truck, rail, ship, or aviation, without processing the freight at the time of the mode change [6]. This method not only improves cargo handling and delivery speed but it also reduces cargo damage [7]. In studies on the use of ecofriendly road-rail intermodal freight transport, researchers have reported various positive effects, such as reducing greenhouse gas emissions by 77.4% and increasing fuel efficiency by 43.48%, compared to traditional truck transportation [8; 9]. Various studies on complex freight transportation systems in the fields of transportation and logistics have been conducted, several of which have improved operational efficiency and transport network performance through collaboration between transport modes [10; 11; 12]. Research and technological development for real-time transportation monitoring are also underway [13; 14]. In the abovementioned ways, intermodal freight transportation systems are being developed in terms of hardware/technical and software/systems.  
Recognizing the importance of intermodal freight transportation systems, countries and companies are developing technologies to dominate the intermodal freight transportation industry in advance. However, decision-making faces difficulties in that it is not possible to accurately predict the technologies that will dominate this industry in the future. In addition, technology has become more complex as it advances. Therefore, many experts use patent documents to extract strategies for technology development or to identify relationships between technologies [15]. Patent documents have thus come to be regarded as a representative data source for forecasting technologies due to patent characteristics (i.e., originality, creativity, and novelty) [16]. Patent documents must be assigned one or more international patent classification (IPC) codes developed by the World Intellectual Property Organization (WIPO) [17; 18]; therefore, based on IPC classifications, various analyses such as identifying cooperative relationships between technical fields, analyzing technology trends, and exploring vacant technologies are possible [19; 20; 21]. Consequently, it is possible to derive practical strategies for technology development.  
Designing a practical R&D strategy requires that researchers make decisions that reflect technology trends. However, industries with advanced technologies are characterized by complexity, variability, and radicalness [22], making it necessary to discover technologies with high potential for future development before competitors do [23]. As an aspect of forecasting future technologies, this study aims to extract managerial insight and future strategies in the field of intermodal freight transportation systems by analyzing the related patent data.