Contents Introduction
In Recent years, with the great construction of the high-speed railway network and the gradual improvement of the conventional railway network in China, Chinese railway transportation has realized development achievements with dedicated passenger high-speed railways as the backbone, conventional railways as the foundation, and intercity railways as the auxiliary. Some conventional railways have improved their speed, changed the lines, reduced trips, and separated passenger and cargo transportation. Also, point-to-point trunk node passenger transport has gradually replaced the universal passenger transport that used to connect urban and rural areas, which has led to the closure of numerous low-grade stations and small passenger platforms as well as the disused or abandoned passenger station buildings and their ancillary facilities. Meanwhile, the deepening of industrial restructuring and capacity reduction measures, and the increase in domestic rail freight volume stagnated led to the abandonment of some existing freight and industrial railway capacity, stations, and warehouses, resulting in a waste of resources [1]. Therefore, updating and reusing these disused railways is an economic demand of railway operating units.
Due to the early construction of disused railways and the continuous expansion of urban areas, railway territory has gradually been surrounded by urban and rural construction land, becoming a negative space that hinders the development of urban transportation and affects the urban and rural landscape to a certain extent [2], [3]. Therefore, updating and reusing disused railways is required for urban planning and development.
A large amount of research and projects has been conducted domestically and internationally on the reuse of disused railways in cities from the perspectives of improving the urban landscape and protecting the industrial heritage with many excellent cases. In recent years, Beijing has attempted to transform some disused railway resources into railway heritage parks [4], [5] and to operate suburban trains on disused railway lines [6], which have achieved good economic and social benefits. However, these practices mainly involve partial transformations of disused resources and space in the urban core area from the perspective of urban renewal, and the reuse strategies derived from a single perspective also have certain limitations. Therefore, there is an urgent academic need to expand the research perspective on the reuse of disused railways.
With rapid economic development, the demands for suburban tourism and leisure are increasing. Due to the relatively unbalanced development of urban and rural public transportation, only some popular scenic spots can be accessed by public transportation, such as tourist buses, suburban buses, and suburban trains. The suburban hinterland with excellent tourism and leisure resources can only be accessed by private cars, and the use of private cars is also limited because of factors such as license plates and traffic restrictions. Utilizing disused and abandoned railways to develop the suburban tourism and leisure industry not only supplements urban self-driving tourism but also helps to alleviate the dense population of the central urban areas of large cities, promotes concentrated development of the suburbs, and assists in achieving the goal of common prosperity for both urban and rural people.
However, since the main responsibility of China's railways is to serve intercity transportation needs or the industrial and mining transportation needs of cities, the selection of its routes is determined based on a combination of transportation demands, construction costs, land acquisition costs, and the terrain along the route (see Fig. 1). The landscape along the railway is not a consideration in the selection of railway routes, and railways cannot connect scenic spots and areas within a region. These reasons have also led to the lag in the development of the railway tourism market in China. In addition, due to the binary land ownership policy between local governments and railway bureaus [7], railway segmentation in urban and rural areas is more apparent, leading to lower spatial quality and poorer scenery along the railway. These factors have resulted in the absence of professional scenic railways in China and reuse cases of disused railway spaces, such as “rail to trail.” When the disused railway transforms to serve suburban tourism, there is an urgent need to analyze and evaluate the landscape quality along its route.
Beijing railway network (Data Source: public information from China State Railway Group Company Ltd.).
Against this background, this study intends to propose and answer two questions.
What kind of landscape can passengers see when taking the train? That is: how to describe and analyze the visual landscape seen by taking conventional trains?
Which landscapes seen along the railway can be denoted beautiful? That is: how to evaluate the visual landscape along the disused railway?
This article takes the Jingmen railway in Beijing as an example and uses GIS tools and analytic hierarchy process (AHP) to conduct research from the following two aspects.
By analyzing the visual landscape characteristics of the conventional railway and combining DEM data, a dynamic visual landscape interface model of the disused railway is constructed to describe the visual landscape seen by passengers on the conventional train and as the basis for dynamic visual landscape analysis and evaluation.
The criteria and indicators for analyzing and evaluating the dynamic visual landscape of disused railways are sorted out and proposed. Taking the typical landscape of the Jingmen railway as an example, the visual landscape along the disused railway is analyzed and evaluated.
The innovation of this article is proposing a dynamic visual landscape interface for disused railways, which establishes a connection between the “seeing” and “perceiving” for passengers and describes the visual landscape they observe. Based on this, this article proposes a feasible plan for analyzing and evaluating the dynamic visual landscape of disused railways, providing an analytical and decision-making tool for reusing disused railways as tourist railways.
This research is organized as follows: Section II introduces the related work, Section III displays the dataset and methods of the research, the results are shown in Section IV, and in Section V and Section VI, there are discussion and conclusion, respectively.
Related Work
A. Reuse of Disused Railway
Railway, as the transportation infrastructure, was born, developed, and declined along with industrialization and urbanization [8]. With deindustrialization in industrialized countries and the development and competition of the transportation industry, the disused and abandoned railway lines appeared in Europe and the United States in the second half of the 20th century [9]. In China, with the rapid development of railways and the adjustment of industrial structure, nearly a hundred railway lines have been disused or abandoned, and the total length of disused railway tracks exceeds 20 000 km [10], [11]. The disused railways cause resource waste and bring problems such as traffic congestion in urban areas and the decline of the surrounding environmental quality [12], [13].
Researchers have conducted extensive research to fully explore the reuse value of abandoned and disused railways [14]. Currently, there are three main modes of reuse for abandoned and disused railways internationally: reuse as transportation facilities, reuse as tourist routes, and reuse as public spaces [11], [15]. Among these three modes, reusing disused railways as transportation facilities involves incorporating them into urban rail transit systems, including conversion into light rail, tramways, and suburban railway lines, or converting them into urban roads to serve the transportation needs of the city [16]. Some of the disused railways that are part of industrial heritage can be transformed into tourist railways or tourist attractions, fully exploring the cultural heritage value of the railways and the natural landscape value along the line [17], [18]. Those railways that are not suitable for continuing to serve transportation functions nor have a strong preservation value, which can be transformed into public spaces to improve the quality of urban public life. This type of reuse usually includes transforming railways into pedestrian or bicycle paths, urban strip parks, green belts, etc. [9], [15], [19].
The disused railway is a complex system that connects regions and nodes. The renewal and reuse of disused railways should not be limited to protecting heritage sites. However, they should be approached from a systematic perspective of the entire route and surrounding areas for comprehensive protection, renewal, and reuse. Eizaguirre-Iribar and Hernández-Minguillón [14] proposed the disused railway system (DRS) and created a comprehensive analysis method (CAM) to characterize and classify disused railway lines of territory as complex systems. Building on the DRS concept, a CAM was developed for analyzing DRSs, which includes three theoretical and methodological underpinnings: disused railway lines as heritage systems; former linear infrastructures as nonmotorized axes; and a balance between transport and other land uses around former railway nodes, to promote sustainable development of disused railways [16].
B. Dynamic Visual Landscape Restoration and Evaluation
Railway sightseeing is dynamic, which needs to consider the speed of the train, the angle and field of view from which passengers observe the scenery outside the carriage. Somogyi and Csapó [18] proposed that visual evaluation should be part of the tourist motivation in their railway passenger landscape preference research. Previous studies have mentioned the importance of visual evaluation of railway passengers, but not considered the perspective inside the carriage, and the use of digital technology can achieve scene simulation restoration. Studies on the dynamic visual quality of landscapes often use photos, videos, and slides instead of on-site landscapes for direct evaluation [20]. Shih and Diao [21] used three-dimensional (3-D) scanning technology to restore scenes and proposed the mutual relationship between railways, architecture, and landscapes reflected in the skyline. Li and Zhu [22] introduced digital technology into the restoration and landscape design of abandoned railways, exploring various possibilities of historical restoration under the background of digital acquisition, protection, restoration, and dissemination through four stages, and provided a reference for the acquisition and restoration methods of dynamic visual landscapes along railway lines.
In terms of visual landscape assessment, previous research has typically used quantitative methods to evaluate the interactions between landscapes [23], establish visual quality indices, and quantify visual landscape quality [24], as well as analyze the dynamic changes in the connectivity of natural habitats through connectivity maps [25]. Visual landscape quality assessments have been applied to rural areas [24], coastal regions [26], [27], and highways [28], but there still needs to be more research in this area regarding the visual landscape quality assessment of railway travel. Selecting key observation points for visual assessment also requires scientific justification [29]. Based on three landscape quality assessment methods, namely landscape vulnerability assessment, landscape sensitivity assessment, and direct landscape assessment, previous studies have found that any of these methods can identify the area with the highest landscape quality within the same region [30].
The application of GIS in railway visual landscape assessment dates to the early days, with Lee et al. [31] exploring the value of GIS in landscape assessment. Zhang et al. [32] used RS and GIS technologies to establish a landscape visual management system along the Qinghai-Tibet Railway. Lin et al. [33] used GIS technology to analyze the distribution of scenic railways in the French railway heritage. Sang and Piovan [34] introduced GIS into the management of the Yunnan-Vietnam Railway heritage. Multicriteria decision-making assistance is a commonly used decision-making tool. The AHP is a widely used multicriteria decision-making method in railway landscape evaluation. AHP is generally used for determining the priority ranking analysis of railway routes [35], [36], analyzing and evaluating railway landscapes with the integration of GIS [37], [38], analyzing land transformation suitability [39], station optimal site selection and scheme selection [40], satisfaction evaluation [41], etc.
Materials and Methods
A. Study Area
The Jingmen railway is located in the western part of Beijing and spans across three administrative districts: Haidian, Shijingshan, and Mentougou, from east to west. The total length of the railway is 53.363 km (Fig. 2, the image shows the location of the Jingmen railway in Beijing and its relationship with the railway network of Beijing. Data Source: public information from China State Railway Group Company Ltd..), with 12 stations: Wulu, Xihuangcun, Shijingshan, Sanjiadian, Mentougou, Yexi, Dingjiatan, Seshufen, Luopoling, Qingshuijian, Datai, and Muchengjian. The railway is divided into two parts: the urban section (19.93 km, from Wulu to Mentougou) and the Menda section (33.413 km, from Mentougou to Muchengjian, Fig. 3. Data Source: Field research.), both of which are single-track nonelectrified railways. Since the Menda section of the Jingmen railway is more representative than the urban section, it is also generally called Jingmen railway, Datai railway, Menda railway, etc. In this article, we take the case study of the Menda section of the Jingmen railway as the example for this research and use its common name, “Jingmen railway.”
The Jingmen railway was initially planned and constructed as a coal transport branch line of the Beijing-Zhangjiakou Railway in 1906. Construction began in 1907, and the section between Xizhimen and Mentougou was completed in 1908. The section from Mentougou to Banqiao was built as part of the Menzhai Railway from 1924 to 1927, also known as the Menban Railway. Between 1939 and 1940, the Japanese army in China repaired and integrated the Jingmen and Menban railways, forming the embryonic form of today's Jingmen railway. In 1957, the Jingmen railway was placed under the jurisdiction of the Beijing Railway Bureau. It underwent several rounds of renovations and expansions, and the section from Xizhimen to Wulu was demolished in 1971, forming the final layout of the Jingmen railway. In 2019, with the transformation of the industry in Men-tougou and the cessation of coal mining, the major section of the Jingmen railway was completely shut down, leaving only the airport fuel supply special train, which runs once every two weeks in the urban section. The Jingmen railway has become a typical disused resource of conventional railways in Beijing.
This research selects Jingmen railway as the study object for dynamic visual landscape analysis and evaluation of conventional speed railways in complex terrains, and the reasons are as follows.
The Jingmen railway located in the typical complex terrain of Beijing: The Jingmen railway is located in the western mountainous area of Beijing's ecological conservation zone, and the line runs along the valleys of the Yongding River and Qingshuijian River. The terrain along the route is relatively complex, with diverse and abundant geomorphological landscapes, and human settlements are relatively concentrated. The railway line starts from Mentougou Station, located on the edge of the city, and passes through the transitional zone between plains and mountains, river valleys, and mountainous gorges. It starts from clusters of mountain villages near the city suburbs and reaches clusters of mining areas in the far suburbs. The diverse and complex terrain conditions along the railway line provide various models for this research.
The Jingmen railway has abundant visual landscape resources along its route: The Jingmen railway is located in the western ecological conservation area of Beijing and the core area of the “Xishan-Yongding River Cultural Belt,” obtaining beautiful scenery and high vegetation coverage along the line. The hinterland of the railway is affluent in ecological and leisure tourism resources. Meanwhile, the line is tailored to local conditions and runs along mountains and waters. It has a total of 75 curves, accounting for 40.9% of the total length of the line. The minimum curve radius of the line is 150 m, and there are 18 small curves with a radius of fewer than 180 m, accounting for 17.3% of the total length of the line. The slower traveling speed and numerous curves provide ample opportunities for dynamic visual sightseeing and diverse viewing angles along the route.
The Jingmen railway is highly valued for updating and reusing disused resources: First, the disused resources of the Jingmen railway keep specific historical and cultural values, reflecting the historical production features of the coal mining and railway transportation industries in Beijing before and after the founding of the People's Republic of China. However, the historical value of these disused resources has not yet reached the level of cultural relics and can be updated and transformed. Second, the disused resources of the Jingmen railway are closely connected to the living space along the line. The railway connects dozens of villages in four towns along the line, which is an important transportation route for commuting and traveling of the residents along the line. Also, it is a significant lever for the concentrated and contiguous development and construction of rural areas. The land ownership along the Jingmen railway is relatively centralized, which is convenient for planning and designing the railway and the surrounding space.
B. Dynamic Visual Landscape Features of Disused Railways in Complex Terrain
1) Dynamic Visual Landscape Features of Disused Railways
The visual landscape of disused railways is different from the general visual landscape. The main difference is that the visual landscape of disused railways is based on the operation of conventional-speed trains, which is dynamic, limited perspectives, continuous, and has strong narrative qualities.
Passengers ride along with the conventional-speed train as it moves, and the objects they observe are in motion relative to the human eye. In dynamic environments, the results of human eye observations are different from those in static environments, which is mainly reflected in two points: as the speed of motion increases, nearby objects appear more blurred, and vice versa (dynamic vision). At the same time, it takes 5 s for human eyes to discern an object clearly, which means that the human eye's ability to distinguish the boundaries of objects changes with the speed of the train.
Unlike self-driving, when traveling by conventional-speed train, the majority of passengers only have a lateral view of the train. When looking out the window, their comfortable viewing angle is ±20°, and the acceptable viewing angle is ±40° [42]. Therefore, the perceived and observable landscapes of the disused railway resources along the line are limited, concentrated within ±40° angle emanating from the railway line (see Fig. 4).
The terrain along the disused railway in mountainous areas is relatively complex, and the limitations of its dynamic visual landscape are more prominent than those in the plains. Slopes and mountain blocks obstruct the line of sight at extremely close range, as well as a multidepth landscape within a suitable viewing distance (see Fig. 5).
Narrativity of the dynamic visual landscape of a disused railway. Because of the only side view angle that passengers have during travel, the landscape ahead is “unknown” to them. The landscape along the line is presented in a linear sequence within the passengers' field of view. The multidepth landscape enters and exits their view at different angular velocities, creating a strong sense of narrativity.
2) Typical Visual Composition: Straight Lines and Curves
Straight section: The straight sections of a disused railway in mountainous areas are often located in wider valleys, riverbanks, and other terrains. A straight route means that train passengers have an equal duration of side-viewing time on both sides (see Fig. 6).
Typical viewshed analysis of a disused railway in a mountainous area (straight section).
Curved section: The curved sections of a disused railway in mountainous areas are more widely distributed than straight sections and often meander along river valleys and mountain slopes. Besides, they are more common in older disused railways. When a train runs on a curved section, at the same speed, the two sides of the train have different angular velocities in the direction of travel. In other words, within the same period of time, the inner side of the curve offers a smaller viewing range but allows for more detailed observation, while the outer side provides a larger viewing range but only allows for a more general observation (see Fig. 7).
Typical viewshed analysis of a disused railway in a mountainous area (curved section).
C. Method of Constructing Dynamic Visual Landscape Interface for Disused Railways in Complex Terrains
Due to the dynamic, perspective-limited, and narrative features of the disused railway visual landscape in complex terrain, evaluating the visual landscape requires not only determining the occlusion relationship of the visual landscape but also clarifying aspects such as effective viewing time, viewing distance, viewing angle, and landscape narrative structure. This article proposes the concept of a dynamic visual landscape interface, which describes the temporal-spatial relationship of the visual landscape along the railway as an unfolded section based on the characteristics of the disused railway's dynamic visual landscape and analyzes and evaluates the visual coupling relationship between disused railway resources and the landscape resources along the railway. Taking the Jingmen railway as an example, this article proposes a method for constructing a dynamic visual landscape interface based on the digital elevation model (DEM) of the railway area.
The DEM can not only analyze the line-of-sight occlusion relationship of the terrain along the railway, but also combine the dynamic, perspective-limited, and narrative features of the disused railway visual landscape with the spatial structure along the railway to reflect the temporal-spatial relationship of the visual landscape. The DSM model provides a more accurate description of surface objects compared to the DEM model. However, when dealing with scales spanning tens of kilometers of a disused railway, the DEM model offers a balance between model accuracy and computational requirements. Therefore, the DEM model serves as the operational foundation for constructing the dynamic visual landscape interface. In this study, ALOS satellite remote sensing images were selected to obtain the raw DEM data, which were then cropped using GIS tools and further edited for 3-D terrain using Rhino software. The spatial resolution of the model is 12.5 m × 12.5 m. We took the 500-m section along the Jingmen railway as the boundary and divided the DEM model into the accurately modeled area of the visual landscape interface and the background area (see Fig. 8), to reduce the calculation volume and simulate the spatiotemporal relationship of the real visual landscape as accurately as possible.
DEM of the Jingmen railway (above) and the localized terrain model along the railway derived from the DEM (corresponding to the blue shaded area in the above image, below).
Based on the preparation of the terrain model along the railway, the dynamic visual landscape of the conventional-speed railway is introduced into the model, distinguishing the observed objects under different viewing distances. The dynamic nature of the visual landscape of disused railways reflects the minimum discrimination scale of passengers for different distances of the landscape when a conventional speed train is moving, which is the minimum observation time (5 s) within the area covered by the line of sight. When a train travels on a mountainous railway, its speed varies due to the curvature radius and gradient of the tracks, resulting in different durations for observing the surrounding landscapes. In order to assess the dynamic visual landscape of the railway in a more consistent and accurate manner, we set the train to travel at a constant speed of 36 km/h on a major section of the Jingmen railway. We defined an observation interval of 5 s (50 m) between each consecutive observation point, and each 10 m along the railway served as an observation point. The observation point served as the starting point for the line of sight, with the vertical surface of the railway line serving as the basis for the dynamic visual landscape interface.
Based on the previous analysis, the limited visual angle of the visual landscape of disused railways refers to the landscape within ±40° pitch angle that can be perceived and observed along the railway line by passengers. The visible object is obtained by cutting the DEM model with the sightline extending ±40° from the observation point, and the different offset distances of the cutting sightlines represent the different viewing distances of the landscape along the railway line. This research sets ±40° as the maximum viewing angle, ±20° as the optimal viewing angle, and five different viewing distances of 100, 200, 300, 400, and 500 m, and obtains the visible points for different combinations of viewing distances and angles, representing the best visible range and the maximum visible range of the observation object in the real visual field of the railway line to reflect the limited visual angle of the visual landscape of disused railways.
The projection of the visible object on the dynamic visual landscape interface is obtained by representing the observed objects at each distance as equidistant points and projecting each point vertically onto the dynamic visual landscape interface. Since the railway line consists of multiple sections with different curvatures, the distribution of the projection points varies with the curvature of the line at observation points with the same distance interval. The density of the projection points reflects the observation time of the landscapes along the railway line during uniform-speed traveling. Changes in the terrain along the line are transformed into linear variations in the projection points. When the projection points are unfolded on the dynamic visual landscape interface, their dispersion, curvature, and occlusion relationships directly reflect the trend of terrain changes and the order of different depths of field and different visual distances entering passengers' views, thus presenting the narrative of the visual landscape along the line on the dynamic visual landscape interface (see Fig. 9).
Complete view of the dynamic visual landscape interface model of the Jingmen railway.
Based on the previous discussion, the construction of the dynamic visual landscape interface for disused railways in complex terrains is based on the dynamic nature, limited perspectives, and narrative characteristics of the dynamic visual landscape interface. The construction method is summarized in Fig. 10.
Complete view of the dynamic visual landscape interface model of the Jingmen railway.
D. Relative Indicators and Establish the Hierarchical Framework
Based on the dynamic visual landscape interface model of the disused railway, this research sorts out the natural and cultural visual resources along the line and introduces the visual landscape features of the disused railway, such as the dynamic nature, angle limitation, and narrative. Besides, based on the reference to previous studies [37], [38], this research conducts an initial selection of indicators through a combination of comprehensive analysis and expert consulting methods for indicator screening, four criteria and 19 indicators are organized. The criteria layer includes dynamic visual sensitivity, natural landscape resources, cultural landscape resources, and visual-landscape coherence. The indicator layer covers the basic semantics, describing the landscape along the Menda section of the Jingmen railway. After the experts compare the judgment matrix in pairs to calculate each indicator weight and pass the consistency test, the dynamic visual landscape evaluation system for the disused railway is obtained (see Fig. 11 and Table I).
To verify the dynamic visual landscape evaluation system for disused railways, representative and diverse landscapes along the Jingmen railway were selected for evaluation. We have considered that the total length of the railway is 33 km, starting from Mentougou to the terminal station Muchengjian, and the human living spaces along the railway have gradually transformed from urban built-up areas to suburban towns and mining areas. The terrain and landforms along the railway include the plain-mountain transition zone, mountainous river valleys, and mountainous canyons, which significantly differ in landscape styles. In order to better explore the overall impact of various evaluative factors on the dynamic visual landscape, we selected six representative scenic areas along the Jingmen railway, labeled 01–06. The selection of these six areas is based on the following criteria.
Scenic beauty: These six areas are the most picturesque along the Jingmen railway.
Different types of landscapes: These six areas can be classified into three types: natural landscapes, cultural landscapes, and a combination of natural and cultural landscapes.
Diverse cultural significance: Each of these six areas represents specific cultural types from the six major cultural categories of Beijing's “Xishan-Yongding River Cultural Belt.”
The specific selected landscape areas are shown in the following Table II.
To accurately capture and reproduce the visual landscape along the railway, this article uses digital cameras to capture typical landscape areas along the line through bidirectional frame-by-frame shooting and panoramic recording and simulates the passenger's perspective at a viewing height of 2.0 m. Some photographs are adjusted using Photoshop to meet the evaluation requirements. The landscape and dynamic visual landscape interfaces of the typical landscape areas are shown in the following figures (see Figs. 12–17). The bird view of the dynamic visual landscape interface is created by overlaying the perspective view of the dynamic visual landscape interface model onto Google Earth imagery. The bright orange and gray lines in the figure represent the visual landscape boundary and transition boundary of the respective landscape area.
The dynamic visual landscape evaluation of the Jingmen Railway, south of Liuliqu Village.
The dynamic visual landscape evaluation of the Jingmen Railway, Dingjiatan Station.
The dynamic visual landscape evaluation of the Jingmen Railway, tunnels of No. 6 to No. 8.
The dynamic visual landscape evaluation of the Jingmen Railway, east of Seshufen Station.
The dynamic visual landscape evaluation of the Jingmen Railway, west of Luopoling Station.
Results
This study used expert evaluation to assess the dynamic, perspective-limited, and narrative features of selected typical landscape areas. Thirty evaluators with three types of backgrounds were hired to obtain objective dynamic visual landscape evaluation results, including landscape planning and design experts, architecture and landscape professional graduate students, and undergraduate students in nonrelated majors. The evaluators first observed panoramic photos of typical landscape areas to understand the overall landscape characteristics of the area. Based on this, they were given a slide of sequential photographs along the route to simulate the dynamic visual landscape experience from a passenger's perspective, establishing a more realistic dynamic, perspective-limited, and narrative experience for the evaluators.
The evaluators used a dynamic visual landscape evaluation system to rate each criterion on a five-point scale: excellent (5 points), good (4 points), fair (3 points), poor (2 points), and very poor (1 point). Based on the comprehensive evaluation results, the dynamic visual landscape scores of the typical landscape areas in the Jingmen railway were obtained (see Table III).
Discussion
A. Overall Evaluation of the Landscape in the Typical Scenic Area of the Jingmen Railway
As revealed by the previous research, the disused railway in the Jingmen railway, which is representative of the complex terrain, possesses natural landscape advantages compared with railways in flat areas. Due to the complexity of the terrain and the early construction age, the railway was built along the contours of the land, resulting in less damage to the terrain and rich diversity of landscape types. The interweaving of natural and human landscapes creates rich narrative features. However, since economic and construction difficulties are the primary considerations during railway construction, rather than sightseeing, the disused railway in complex terrain is not fully compatible with the surrounding landscape. The railway landscape lacks planning, and the potential for railway tourism has not yet been fully explored.
B. Analysis of the Dynamic Visual Landscape Evaluation Results for Typical Landscape Areas in the Jingmen Railway
The analysis of the results of the dynamic visual landscape evaluation of the typical landscape areas in the Jingmen railway reveals the order of the dynamic visual landscape scores of the six typical areas, which is 05 > 04 > 01 > 06 > 02 > 03. Among them, the ranking of natural landscape resources is 04 = 01 > 06 > 02 > 05 > 03, while the ranking of human landscape resources is 05 > 03 > 02 > 06 > 01 > 04. Since the 03 Dingjiatan Village only has human landscape resources, its natural landscape resource conditions are average condition, and the level of C_17 (Hierarchical nature of visual-landscape perception) and C_18 (Narrative drama of visual-landscape) in the B_4 (Visual-landscape coherence) is poor, the overall score is relatively low. The natural landscape resource conditions of 01 and 04 are superior, although they lack human landscape resources, and both have good dynamic visual sensitivity and visual-landscape coherence. 05 East Shiguyan Village has both natural and human landscape resources and has the best experience of viewing the scenery by train, as it has a long observation time, a suitable observation distance, and the best observation angle in dynamic visual sensitivity. Besides, the visual-landscape coherence has a high level of hierarchical nature of visual-landscape perception and great narrative frame and integrity in 05 East Shiguyan Village, thus obtaining the highest score in the evaluation of dynamic visual landscapes.
C. Analysis Method for Disused Railway Landscapes: Dynamic Visual Landscape Interface
Regarding the question of “How to describe and analyze the visual landscape seen by taking conventional trains?,” two common methods have been used in previous research on visual analysis and evaluation of railway corridor landscapes.
Relying on GIS to analyze the spatial distribution characteristics of railway landscapes, mapping the spatial structure of railway landscapes, and then describing the visual landscapes seen when traveling on conventional trains [28], [33]. This method can describe the distribution of the railway landscapes in the corridor and make the reuse planning of the disused railway accordingly, but it is difficult to describe the microscopic features of the railway landscapes and may not sufficiently support railway landscape design.
Establishing AHP evaluation criteria for railway landscapes and combining GIS analysis: his method involves developing AHP evaluation criteria for railway landscapes and employing GIS to analyze and map the spatial distribution of landscape features [37], [39]. This method not only describes the spatial structure of railway landscapes but also captures variations in the quality of visual landscapes across different areas within the corridor. However, this method is not based on the actual observation perspective of passengers during train travel and cannot precisely describe passengers' real viewing experiences.
The dynamic visual landscape interface proposed in this research is a modeling analysis that combines the dynamic visual features of the view angle of passengers on a conventional-speed train with the DEM model. It describes and analyzes the visual coupling relationship between the idle railway and the landscape resources along the railway in the form of a facade that unfolds the temporal-spatial relationship of the visual landscape along the railway. The dynamic visual landscape interface describes the temporal-spatial sequence of the railway landscape in the passenger's view angle and establishes a medium for the static landscape along the railway and the dynamic view experience of passengers.
D. Dynamic Visual Landscape Evaluation System
The dynamic visual landscape evaluation system proposed in this research is based on the simulation of the passenger viewing experience on the dynamic visual landscape interface. The significant difference from traditional landscape visual evaluation is that this evaluation system attempts to quantify the spatiotemporal relationship of the visual landscape and incorporate it into the indicator calculation. Due to the dynamic, perspective-limited, and narrative features of the disused railway visual landscape in complex terrain, a mechanical and static visual observation of the landscape along the line cannot fully reflect the real landscape experience when taking the train. Through the dynamic visual landscape evaluation of typical landscape areas along the Jingmen railway, it is known that the actual experience of passengers viewing the scenery on a conventional train is not only related to the richness of the scenic resources but also to indicators that reflect the dynamic visual sensitivity and visual-landscape coherence.
The dynamic visual landscape evaluation system still has some shortcomings, and descriptions of landscape scale and seasonality [43], [44] need further improvement. For example, the evaluation criteria include the “vegetation coverage” indicator, attempting to describe the scale of vegetation landscapes in railway scenery. However, limited by research methods, vegetation coverage can only be assessed through 2-D data, such as satellite and aerial photographs, and it cannot reflect the actual observation effect of vegetation in a 3-D perspective. At the same time, the “green period” attempts to describe the observable time of railway vegetation landscapes throughout the year, but due to the short mileage of the selected Jingmen railway, this indicator does not vary significantly at various selected typical landscape locations.
Conclusion
Against the backdrop of some conventional railways being disused and the continuous growth of suburban leisure tourism demand, there is a requirement in China to use the existing disused resources of conventional railways for tourism. However, these disused railways encounter problems such as poor compatibility between the route and the scenery and uneven landscape quality along the route. In light of this, this article focuses on two issues.
How to describe and analyze the visual landscape seen by conventional trains?
How to evaluate the visual landscape along the disused railway?
By analyzing the dynamic visual features of train passengers and combining them with DEM data, a railway dynamic visual landscape interface model was constructed to evaluate the visual-landscape relationship and dynamic visual landscape evaluation. This research combines the dynamic nature, perspective-limited, and narrative features of visual landscapes with the terrain along the route by analyzing the dynamic prerequisites for viewing scenery while riding the train, and constructs a dynamic visual landscape interface model, accurately simulating the actual viewing experience of passengers while taking the train and constructing a spatiotemporal relationship of viewing.
Based on the dynamic visual landscape interface model, criteria and indicators for evaluating dynamic visual landscapes along disused railways were organized and proposed. The typical landscape of the Jingmen railway was used as an example for verification. The evaluation results show that the evaluation of the scenery along disused railways cannot be separated from the premise of the viewer's movement. Only the landscape that meets the requirements of the train section's travel speed, appropriate viewing distance, and viewing angle can be considered a railway landscape.
The innovation of this study contains two aspects.
Innovation of research object: In China, the problem of disused conventional railways has emerged recently with the development of the times, and there has been little research on the reuse of disused railways. Similar research mainly focuses on railway heritage conservation, and the research objects include only a few heritage railways, such as Jing-Zhang railway, China Eastern railway, Yunnan-Vietnam railway, Jiaoji railway, etc. There has been little research on the numerous disused conventional railways without heritage conservation value. The research object of this study, the Jingmen railway, is a typical representative of these disused conventional railways. These disused conventional railways are generally well-preserved and suitable for renewal and reuse for diverse needs, rather than being demolished and rebuilt as greenways. The selection of the research object is one of the main innovative points of this article.
Research on the dynamic visual landscape interface model combining macro- and micro-perspectives based on the passenger's viewing. Most existing research on railway heritage conservation and landscape analysis uses GIS to evaluate the landscape quality of the entire railway corridor. This article analyzes the limitations of the actual viewing perspectives of passengers when taking the train and proposes that the visual landscape of disused railroads is dynamic and continuous, with limited perspectives, and has strong narrative qualities. Based on these landscape characteristics, the proposed dynamic visual landscape interface model contains the micro-level passenger viewing perspective and the macro-level geographic landscape. The railway landscape evaluation based on this model can more accurately reproduce the actual scenic experience of passengers.
Based on the research in this manuscript, it is known that when utilizing the leisure and tourism value of the disused resources of the conventional railway and planning the railway landscape along the line, it is necessary to conduct investigations and organize the railway landscape in advance. Based on the appropriate train operating speeds and reasonable engineering costs, the main scenic areas along the railway line should be planned to ensure that the main scenic resources are within the appropriate viewing angle of the train. When an existing railway line is renovated, and tourist trains are put into operation, train operations can be arranged based on the dynamic visual landscape interface model in the context of the temporal-spatial relationship of the landscape. In areas where the landscape resources are abundant but the dynamic landscape viewing angle is not ideal, increasing train stops and transfers can be considered to expand the ways of sightseeing and enhance the viewing experience.
Furthermore, the dynamic visual landscape analysis and evaluation proposed in this article were completed under the premise of complex terrain. For railways with less visual landscape changes influenced by the spatiotemporal relationship, such as those in plain terrain, their railway landscapes exhibit relatively little change on the dynamic visual landscape interface. Therefore, further research is needed to explore the planning path of railway landscapes in plain areas based on the dynamic visual landscape interface. We will also consider multiscale factors to evaluate the spatiotemporal effects [45], [46], [47] in future work.
ACKNOWLEDGMENT
Research on the reuse of idle resources of conventional railways in the Beijing-Tianjin-Hebei region based on the coupling of “resource renewal-leisure demand,” Nos.22YJC630150.