1. Introduction
Transportation is the foundation for the survival of human society and is a safeguarding industry in the economic and social development of a region [
1]. Accompanied by the development of national transportation infrastructure, the complex modes of transportation work together to form an efficient, comprehensive transportation system, which is both an important foundation for the construction of a strong transportation country and an inevitable choice to promote the opening up and collaboration with the outside world [
2]. As an important node for realizing Asia–Europe connectivity, Xinjiang is an important link for promoting the cross-border transportation market and developing cross-domain logistics in Central Asia. These factors are of great strategic significance in realizing China’s economic stability and prosperity.
At present, along with the continuous promotion of the “One Belt, One Road” initiative, Xinjiang has changed from the end of the national road network in the west to a bridgehead for opening up to the west and was identified as the core area of the Silk Road Economic Belt in 2015 [
3]. Combined with Xinjiang’s development orientation of “linking the east with the west”, the Ministry of Transportation in Xinjiang sought to build a strong pilot traffic system and facilitate the building of a cross-regional comprehensive transportation channel construction to support national internal and external circulation and enhance the country’s facility-connectivity capacity. At present, all 15 first-class national ports in Xinjiang have access to secondary roads and above, two ports have access to railroads, and other cross-border railroads and high-grade highways are entering the planning or design stage one after another. With China’s bilateral and multilateral trade cooperation with Central Asian countries continuing to deepen, the demand for a Xinjiang–Central Asia five region transportation market has become increasingly strong. However, according to the survey, the overall quality of transportation infrastructure in the five Central Asian countries is at the lower-middle level (
Table 1), and the level of regional connectivity has become a bottleneck restricting cross-border openness and cooperation [
4]. Xinjiang and the five Central Asian countries are located in the same hinterland of the Eurasian continent. The sparse road network is widely distributed, the node spacing is large, the road network accessibility is low, and the regional development is presented as a loose polycentric spatial structure. In addition, the mechanism of the supporting role of Xinjiang’s transportation infrastructure development on the national economy and social development is significantly different from that of the inland areas. And the economic and social geographic phenomena of regional spatial units under different spatial scales are also closely related to the spatial units of neighboring regions. Therefore, the analysis of the neighboring effects of transport corridors and road network resources of multi-scale spatial units is crucial for the rational planning and optimization of the level of connectivity between Xinjiang and Central Asia’s five countries’ transport infrastructures.
Along with the further development of the “flow space” theory, basic transportation planning research has gradually crossed over to the direction of spatial structure [
5,
6] and spatial and temporal evolution [
7,
8]. The different spatial and temporal scales of road network morphology variables on the economic development of the region along the measurement conditions are caused by the variability, and determining the spatial scope of the multi-scale region to build the effectiveness of the transport corridor articulation has become an important frontier field of transportation management [
9,
10]. Hence, further in-depth research on this area is necessary. In the historical study of transportation road network optimization, algorithms are mostly used to optimize the microcirculation within the urban traffic zone [
11]. In contrast, optimization studies with cross-border transportation corridors as the research object have been relatively fewer. Determining how the existing road network structure can be used to improve the access capacity of transportation infrastructure services to achieve the overall optimization of the road network has become increasingly urgent.
As one of the important indicators for measuring the service level of regional transportation infrastructure, traffic accessibility has been widely used in the research of urban land use [
12,
13], transportation road network optimization [
14,
15], and spatial transportation planning [
16,
17]. Scholars at home and abroad have used the accessibility index to assess the spatial effects of transportation infrastructure, focusing on the evolution and spatial–temporal convergence effects of accessibility brought about by the improvement of transportation road networks of different scales [
18,
19]. Relevant research has concentrated on the county and city levels [
20,
21], and research on cross-regional transportation networks and accessibility has been limited. In terms of research methods, those based on transportation accessibility are mainly quantitative, including GIS spatial technology [
22], network analysis and cost raster weighted integration [
23], economic gravity [
24], weighted regression [
25], and weighted travel time [
26]. With the development of spatial measurement technology, the inverse distance weight method of spatial measurement, coupled coordination model, etc., have also gradually become important means of transportation accessibility research. However, the above accessibility research methods are mostly based on the time-cost model to consider the layout of a certain urban node, and pay relatively little attention to the strength of transportation links between different nodes (especially between cross-border regions).Currently, the literature on the Belt and Road initiative has focused on transport infrastructure along the Belt and Road and few studies have focused on transport accessibility and optimal construction of transport corridors. These studies have focused on the economic spillover effect [
27,
28], cross-border investment (FDI) growth [
29,
30], and the strategic value of infrastructure construction [
31,
32], and the relatively economically developed city clusters along the Maritime Silk Road [
33,
34]. Less research has focused on the relatively backward land transport along the Silk Road Economic Belt, with particular focus on the Northwest Corridor Belt [
35] and the entire Silk Road Economic Belt [
36] as the starting point for discussion.
In summary, the current research on the model algorithms related to traffic accessibility and road network optimization has been relatively perfect. However, research on their application to cross-border transportation, especially from the perspective of China and the five Central Asian countries, has been lacking. How can we evaluate the soundness of the inter-regional cross-border transportation corridor network after the given cross-border infrastructure is completed? What role does transportation infrastructure play in cross-border economic exchanges?
In order to answer these questions, this paper takes the “mobility space” theory as a benchmark, which takes the optimization of cross-border road networks between Xinjiang and five Central Asian countries as a main line and measures and analyzes the development status of cross-border transport corridors and the backward projection after optimization in two dimensions, so as to provide data references for the optimization of cross-border transport corridors between China and the five countries of Central Asia (as shown in
Figure 1). The main contribution of this paper is twofold:
Using the transportation accessibility assessment model combined with policy orientation, it points out the existing problems of the current Xinjiang–Five Central Asian countries transportation corridor;
Analyzes the influencing factors leading to the limited accessibility of Xinjiang–Five Central Asian countries in combination with the current situation of Xinjiang’s cross-border port infrastructure construction;
Analyzes the economic effects of improved transport corridors by using backward projection and the results of the gravity model.
The rest of this paper is organized as follows:
Section 2 provides an overview of the study area and the model used and introduces the data sources.
Section 3 analyzes the spatial pattern of traffic accessibility in Xinjiang–Central Asia’s five cross-border transport corridors and identifies the problems of the current Xinjiang transport road network.
Section 4 optimizes the cross-border transport corridors for the problems of the existing road network, analyzes their feasibility comparatively, and conducts economic linkage measurement analysis of the transport road network before and after optimization by using the gravity model to explore the internal logic mechanism between road network and economic and social development to provide theoretical support for the optimization of the transport infrastructure under the conditions of a sparse road network. Finally, conclusions are drawn, highlighting the shortcomings and potential for future research.
5. Discussion
This paper measures the level of cross-border transportation corridor construction between Xinjiang and five Central Asian countries by applying the accessibility factor. The study shows that, on the whole, the accessibility status is positively correlated with the level of transportation infrastructure construction and city size and negatively correlated with the city distance, with an obvious distance attenuation effect. In terms of the accessibility sub-region of the study object, the high-accessibility areas are all located in Urumqi and its surrounding areas at the southern edge of the Junggar Basin, while the low-accessibility areas are located in the south of the Tarim Basin and the Kunlun Mountains. The accessibility level from each prefecture in Xinjiang to the five Central Asian countries shows a strong north and weak south trend, with a “corridor” spatial layout.
From the backward projection of the optimization of the regional planning road network, the construction of the G3033, G0711 Wuwei Highway, G219 Wensu-Zhaosu section, and Yi-A railroad will improve the phenomenon of “east-west access but north-south inaccessibility”, which will drive the accessibility of the Aksu region and the urban agglomerations of the Southern Xinjiang region to the cross-border border crossings. The construction of the Baktu–Ayaguz project and the Sino–Japanese–Ukrainian Railway project will initially realize the road network pattern of “one axis (Lanzhou–Xinjiang Railway and Lanzhou–Xinjiang High-speed Railway), three outbound routes (the central Lanzhou–Xinjiang line, the northern Linha line, and the southern Geku line), two loops (the northern and southern Xinjiang loops), and two outbound routes (the Alashankou and the Khorgos Ports), comprehensively upgrading the cross-border transportation corridors of Xinjiang. The absence of major changes before and after the optimization of the road network at the Mulzat crossing implies that the optimization of cross-border transport corridors requires the joint efforts of the countries on both sides, which demonstrates the importance of coordinated construction of interregional transport corridors.
Therefore, Xinjiang must rely on policy opportunities, give full play to the collection and distribution functions and hub advantages of the China–EU train consolidation center, and build a “channel + hub + network” system to build a logistics hub system, forming a “fast inbound and outbound, smooth north and south of the border, inbound and outbound, within the border ring up” as the main skeleton network of large channels and provide strong support for Xinjiang’s high-quality economic development and integration into the new development pattern. Specific recommendations are as follows:
- (1)
Create the core area of the Silk Road Economic Belt, from “economic and trade cooperation + transportation corridor + logistics hub” organic integration. At present, the Asia–Europe Land Bridge Economic Corridor around the transportation road network has been perfect. However, to promote economic and trade exchanges between China and European countries, the construction of logistics corridors in the region needs to be sped up. China’s economic corridors to Central Asia are mostly still in the initial stage of construction, so the level of construction should be improved, the construction process should be accelerated, and the goal of access should be realized as soon as possible;
- (2)
The focus is on enhancing the construction of the southwest corridor in the core area of the Silk Road Economic Belt and strengthening the level of transportation accessibility in the desert hinterland, such as the Hotan and Kashgar regions, as well as the southern part of the Bayin’guoleng Mongol Autonomous Prefecture. Due to the natural geography of deserts or high mountain ranges, the urban characteristics of “large dispersion and small agglomeration” vastly increases the distances between cities and towns in this region. The time cost is higher than in other regions, and thus, economic links between urban development and urban development are heavily dependent on the ability of transportation to reach them;
- (3)
To further improve the construction capacity and level of the middle corridor of the Silk Road Economic Belt, the construction of high-grade railroads and highways is moderately ahead of schedule, and a highly efficient combination of railroads and highways is being built. The Tianshan Mountain Range is located in the middle corridor of the Silk Road Economic Belt, and the geological conditions are harsh; hence, determining the most suitable construction technology for the complex terrain and the breaking of geographic zoning are the most important factors in the construction of the transportation road network in the core area. Therefore, improving the level of construction in this region will not only promote the economic development of the desert hinterland and mountainous towns in the core zone but also enhance the level of accessibility of the core zone to Central and West Asian countries, such as Kazakhstan, Bangladesh, China, India, and Myanmar;
- (4)
Mutual political trust is the basis for cooperation between the two countries. Because of its unique geographical location, Central Asia has become the center of international geopolitical competition. Political stability is a prerequisite for economic development, and transportation development is also a prerequisite for political stability. The shelving of the Sino–Japanese–Ukrainian Railway could be attributed to political reasons. Therefore, in terms of political mutual trust, strengthening bilateral communication, avoiding violent conflicts, establishing and maintaining friendly partnerships with Central Asian countries, and working together towards the goal of realizing intra-regional interconnection and economic prosperity, unity and cooperation, and common development are important.
6. Conclusions
This paper explores the overall spatial and local spatial evolution structure of cross-border transportation access in Xinjiang through the analysis of the temporal accessibility distribution pattern of Xinjiang–Central Asia five countries and finds that the development of Xinjiang and the five countries in Central Asia presents a loose polycentric spatial structure. It is generally believed that transport corridors have a strong positive correlation with regional economic development, and this paper utilizes the gravity model to carry out the analysis of economic linkage measurement and elucidate the mechanism and driving force between transport corridors and regional economic space. Finally, based on the overall spatial structure of cross-border transport corridors within Xinjiang Autonomous Region, Xinjiang, and the five Central Asian countries and the real conditions of the formation of transport corridors, this paper conducts a backward deduction in conjunction with the planning of the road network project to form an optimization strategy by considering the measurement of the economic linkage.
Therefore, this study breaks through the basic theories and methods of road network optimization under the sparse road network model, provides management support for the optimization of the Xinjiang–Central Asia road network and the formulation of regional multilateral policies, and enriches the related research on cross-border transport corridors in western China. In addition, this study is of great practical significance for accelerating the integration of Xinjiang into the new development pattern of the “double cycle”, the implementation of the Western development strategy, the deployment of the Belt and Road Initiative, and the construction of cross-border transportation connectivity.
However, this study only focuses on Xinjiang and five Central Asia countries. It does not comprehensively cover Xinjiang–Europe, China–Mongolia–Russia, and Xinjiang–South Asia, and, hence, might not cover the entire Xinjiang Uygur Autonomous Region’s “port economic belt.” In the future, economic and trade cooperation between Xinjiang and Europe, Mongolia and Russia, Southeast Asia, and South Asia should be explored further.