The Changsha Historic Urban Area: A Study on the Changing Accessibility of the Road Network

Abstract

In this study, we used a complex network analysis to examine the accessibility features of changing road networks in historic urban areas. We aimed to discover the pattern of evolution after studying the accessibility of the road network in the Changsha historic urban area over four periods of time. The results were as follows: the layout of the urban road network shows repetitive cluster–parent–subsidiary development, which provides evidence of adaptive adjustment in urban road development; vulnerability has been kept low in the changing urban road network, while the spatial framework of the Changsha historic center is fixed; the evolving urban road network generally shows a deteriorating level of stability, which is largely affected by the shape of the network; the degree centrality (1877, 1.87%; 1917, 1.32%; 1987, 1.85%; 2021, 1.51%) of the urban road network shows a decreasing trend, meaning that the network is generally becoming more balanced in its evolution; and the accessibility of land plots currently used to preserve cultural relics and historic sites remains at a medium to low level, and improvements are needed for some plots. In analyzing the changing accessibility of urban roads in the historic center of Changsha city, two major problems for road renewal were identified: (1) unbalanced development of the urban space due to capital-based projects and (2) providing an appropriate increase in plot accessibility while putting equal emphasis on the protection of the spatial framework in the historic urban area. We conclude that a dynamic review of urban road network accessibility and its targeted optimization are of great significance for the protection and development of Changsha’s historic urban area.

1. Introduction

In historic urban areas, roads are built to meet human needs and should develop into a stable and adaptive overall network structure over time [1]. Such small-scale structures are human-oriented and reflect the economic activities of the residents at the time [2]. As society continues to grow, the city area multiplies, and the focus of road design is shifted to cars. This pattern allows more human interactions, provides less traffic exchange space, and makes cities less enjoyable places to live in [3]. At the same time, the rapid urbanization process has brought conflicts on topics including urban function, structural evolution, economic growth, and the conservation of historic sites. Hence, protection of the spatial pattern of historic urban areas and making good use of historical relics while transforming and upgrading the modern urban road traffic system have become urgent issues. Considering that historic urban areas are usually the urban centers of cities, this problem is receiving more attention. It is widely understood that urban transportation is the major factor influencing economic activities. The accessibility of the transportation network determines how closely different areas within a city are connected to each other [4], optimizing the logistics system to avoid energy waste [5]. Proper space–human flow guidance helps to not only activate the economic and social value of the historical heritage but also enhances the diversity of tourism attractions, making the city more attractive to tourists [6]. Hence, the land value in the urban center will also increase. China attaches great importance to the protection of historic urban areas. In doing so, financing has become the key to protecting cultural relics. At the same time, cultural tourism is an integral part of the national economy. Therefore, well-organized transport guidance is key to the protection and development of relevant resources in cities.

Therefore, we believe that understanding changes in road accessibility in historic urban areas and their intrinsic driving factors are of significant importance, both theoretically and practically, to the overall conservation and development of historic urban areas.

Previous studies on road transport in historical urban areas have focused on three aspects: theoretical framework, planning strategy, and methodology. Regarding the first aspect, transport studies on historic urban areas were conducted earlier by western researchers. For example, the ‘shielding’ and ‘tranquility’ theories were developed in 1960 based on the human–vehicle layout pattern in old towns, and the Hoi An Protocols for Best Conservation Practice in ASIA released by UNESCO in 2005 outline transportation studies against the backdrop of the protection of historical and cultural heritage.

In China, the Standard of Conservation Planning for Historic urban areas propose that the display and utilization of historical elements should be enhanced and the use of space should be improved through a transport optimization project [7]. Key research achievements cover the topics of ‘public transportation’ [8,9], ‘green transport’ [10], ‘dynamic renewal’ [11], and ‘adaptive regulation’ [12,13], among others. In terms of a planning strategy, emphasis has been given to zone control, urban transport system oriented coordination of historical site conservation and city transport development [14], a protection-prioritized transport planning policy, the fundamental mindset of local road adjustment, transport solutions based on a diversified set of tools [15,16], the development of a comprehensive and efficient transport system that integrates historical urban areas [17], and the improvement of road transport to guide the development of historical urban area based on supply and demand [13]. In terms of methodology, quantified research on road transport in historical urban areas is gaining more attention. Tools used have included the analytic hierarchy process [12], space syntax [18], and the fractal dimension measurement algorithm [19]. In recent years, interdisciplinary studies on transport planning and complex networks have been promising, covering topics such as expressways, rail transport, urban rapid transport, rural roads, and residential roads. This research has been widely applied to find solutions to traffic congestion, sudden and destructive emergencies, and the matching of traffic and land development [20,21,22,23,24]. From the above mentioned analysis, it was concluded that further research on the intrinsic driving forces behind the transport evolution mechanism should be supplementary to the building of a theoretical framework for transport studies in historical urban areas. The development of a time-space synergy and dynamic development strategy should promote further understanding of planning strategies, and few studies have looked into the evolution of transport accessibility in historic urban area using a complex network analysis in the methodology. Consequently, this paper intends to analyze the road transport accessibility features of the Changsha historic urban area over four time periods using the complex network analysis, aiming to reveal the road transport accessibility evolution features, the internal causes of this process, and the current accessibility of cultural relics and historical sites. It is believed that this study will enhance the overall protection and development of the historical urban area of Changsha.

2. Research Subject and Methodology

2.1. Selection of, and Brief Introduction to, the Research Subject

Located in the middle reaches of the Yangtze River, Changsha (111°53′–114°15′ E, 27°51′–28°41′ N) is situated on the low-lying alluvial plain area on both sides of the Xiangjiang River. It has a subtropical monsoon climate. The architecture-friendly geographical conditions and livable climate of the area have allowed the city to develop over a long period of time. Ever since Changsha was first built as a city in the Spring and Autumn and Warring States Period, throughout history, it has been selected as the location of local authorities, including Jun, Guo, Zhou, Fu, Lu, Ting (names of Chinese administrative divisions in various historic eras). In 1664, Changsha was established as the provincial capital of Hunan province, further strengthening its central position in the historical and economic development of central China. Over more than 3000 years of urban development, the development of the Changsha historic urban area has continued, and this process has been the core of history-based urban expansion and the basis of the city’s spatial framework, despite the area suffering from repeated wars and subsequent disruption due to city construction initiatives [18]. Changsha is famous for the many historical and cultural sites it houses and was recognized among the first batch of National-level Historic Cities by the State Council in 1984. Therefore, the city’s key socio-political status, its solid foundation in cultural heredity, and the hyper-steady development in the geographic space in this location were the main reasons for using Changsha as our research subject. Reference was made to the historical and cultural protection area listed in Changsha: A City of History and Culture, the public understanding of the historical urban area of Changsha, and the city’s construction records in deciding the research scope. As a result, the research scope was determined to be the area surrounded by Xiangya Road in the north, Furong Middle Road in the east, Baisha Road in the south, and Xiangjiang River in the west (see Figure 1), as shown on the map for the year 2021 with corresponding historical adjustments according to evolution and expansion records. The representation principle was followed when picking the time period: before the Eight-Nation Alliance Invasion, the spatial layout and structure of non-coastal Chinese cities were relatively stable. As a result, the 1877 Changsha map [25] is considered to be representative of the end of the feudal society. Considering the changes in the social structure and the impacts of war on city construction, the 1914 Changsha map [25] was taken to represent the early Republic of China era. City roads were improved after 1920, while the city wall was demolished to build a ring road in a bid to enhance road transport and improve the openness of the city proper. Socio-economic development became stable after the founding of the People’s Republic of China, in particular, after the city’s development was turned open to the world as the country moved from a planned economy to a market economy. Consequently, the 1987 and 2021 Changsha maps [25] were selected to represent, respectively, the end of the planned economy era and the market economy era, which is still developing (see Figure 2). This study focused on the spatial topological relationship of land use, so the difference in map resolution had very little influence on the results.

2.2. Research Methodology

2.2.1. Literature Studies and Field Investigation

A variety of literature were investigated to understand the history of Changsha, the urban spatial layout features, and the changes in social backgrounds. The key periods in Changsha’s history were selected as research subjects of this paper. A field investigation methodology was applied to investigate the understanding of Changsha’s historic urban area among its citizens, and this allowed the research subject and scope of this paper to be further narrowed with reference to the conservation area specified in the Conservation Planning of Changsha Historic urban area.

2.2.2. Methodology Used for Network Model Building

A network model is composed of ‘nodes’, which reflect the entities that exist in the real world, and ‘lines’, which represent the relations or interactions among such entities [26]. In this paper, the accessibility of urban roads is transformed into the nodes and edges of the network, and the urban road structure is described in network form.

2.2.3. Complex Network Analysis

The mechanism behind the network of ‘nodes’ and ‘lines’ can be understood and transcribed systematically through the complex network analysis [27], while the structural indicator system can be used to quantify and evaluate the spatial network of roads in the historic urban area. This study based its analysis of the road network’s structural layout, spatial vulnerability, spatial stability, spatial balance, and accessibility to the historic area on an analysis of the road space network structure. We largely relied on quantified results to identify the features of road transport space evolution in the historic urban area and their internal driving forces to provide solutions for the improvement of the conservation and utilization of historical sites.

(1)

Building the Semantic Model

The complex network method was employed to determine the ‘node’ element of the road (between two intersections) and the ‘line’ element (direct connection between adjacent intersections), which means if a road (node) is connected to an intersection, it is considered to have a connection relationship (line). Based on the urban road-space relations in the historic urban area, a 1-modular data matrix on the road-to-road relationship was established. This was introduced to Ucinet, a network analysis software program, to produce the 1-modular network matrix on the road-to-road relationship.

(2)

Establishing the Model

Software, such as cad and gis, were used to digitalize the selected maps according to the syntactic model building principles (Figure 3). This resulted in a 1-modular relations matrix on the road-to-road relationship. The matrix was then processed by Unicet to produce the 1-modular network matrix on the road-to-road relationship, which was also processed for visualization.

(3)

Indicator System

The overall accessibility of the road network in the Changsha historic urban area is represented by the vulnerability, stability, level of balance, and connectedness of the network. Those indicators were calculated based on the 1-modular network matrix on the road-to-road relationship. The node density and point of contact were used to reflect the vulnerability; the network density and k-core were used to reflect the stability; the degree center potential and middle center potential were used to reflect the degree of balance; and the degree centrality of roads connecting to the historic conservation area was calculated to reflect the accessibility of the area.

 (a)

Node Density

Node density refers to the degree of connection between individual nodes in the overall network. It is calculated as the ratio of the existing relations of a single individual node in the network to the total number of nodes in the network. The lower the density value is, the higher the level of vulnerability in the network. The formula is as follows:

D = m/[n(n − 1)]

(1)

In Formula (1), D is the network density, m is the number of relations existing in the network with connections to the node in question, and n is the total number of nodes in the network, i.e., the scale of the network.

 (b)

The Point of Contact

If a point of contact is removed, the network will break down into a couple of separate parts. Therefore, it is widely accepted that the ratio of these nodes to the total number of nodes in the network can be used to access the level of vulnerability in the network.

 (c)

Network Density

The network density represents how closely the nodes are connected to each other in a network. Its definition is the ratio of the connections a node actually owns to the maximum number of lines it may own. The network density can be used to evaluate the degree of network completeness. The formula used is as follows:

P = L/[n(n − 1)/2]

(2)

In Formula (2), P is the network density; L is the number of connections that actually exists in the network; and n is the number of nodes that actually exists in the network.

 (d)

Lambda Collection:

The overall stability of the network structure was measured by analyzing the edge correlation degree of the network hierarchy.

 (e)

k-core

k-core (k = 1, 2, 3…) was used to calculate the local stability of a measurable network, where the larger the k value, the more local network components with stable structures were contained in the network and the higher the overall network stability level. In other words, the network stability is positively correlated with the k value and the k-core ratio.

 (f)

Degree Center Potential

The Degree Center Potential was used to analyze the degree centrality of the overall network and to test the general degree of balance for a certain relationship in the network structure, where the higher the center potential ratio, the more concentrated the roads are, which also means that the network is less balanced. The formula is as follows:

$$\mathrm{C}=\frac{{\sum }_{\mathrm{i}=1}^{\mathrm{n}}\left({\mathrm{C}}_{\max }-{\mathrm{C}}_{\mathrm{i}}\right)}{\max \left[{\sum }_{\mathrm{i}=1}^{\mathrm{n}}{\mathrm{C}}_{\max }-{\mathrm{C}}_{\mathrm{i}}\right]}$$

(3)

In Formula (3), C_max is the maximum value of the degree centrality of the nodes in the network, while C_i is the centrality value of node i.

 (g)

Degree Centrality of Nodes

The degree centrality of nodes refers to the central status owned by the research subject in the social network. It is calculated by the connections of a node with other nodes in the network relationship. In other words, the higher the degree centrality is, the more connections the node has, and the higher the status of the network center is.

3. Results

3.1. Analysis of the Overall Space Layout Evolution of Urban Roads in Various Periods of Time

Figure 4 shows that the urban road-space structure in 1877 had the most concise and balanced cluster shape, meaning that information exchange was governed by political and military activities. Under the feudal centralization system, urban traffic information transmission was the most centralized and balanced. In 1914, the parent–subsidiary pattern of development started to emerge, and the overall shape was the most diverse. The main reason for the emergence of subsidiary clusters was the rapid development of new areas after the removal of the city wall and the loose road connection between new and old areas. In 1987, the cluster-shaped pattern reappeared, while in 2021, the parent–subsidiary pattern again took the lead. It is concluded that the road-space network structure evolution in the historic urban area shows clear and repetitive development of ‘cluster–parent–subsidiary–cluster–parent–subsidiary’ patterns, which reflects the adaptivity in the road system to city space renewal. On the other hand, it shows that the road layout structure in the historic urban area features a dynamic ascending spiral.

3.2. Vulnerability Analysis in Various Periods

3.2.1. Node Density Analysis in Various Periods

Table 1. Road Node Density in the Changsha Historic Urban Area in Various Periods.

	City Urban Roads in 1877	City Urban Roads in 1914	City Urban Roads in 1987	City Urban Roads in 2021
Node Density (Min.)	44.36	0	37.98	35.8
Node Density (Ratio of Min.)	0.4%	0.1%	0.2%	0.1%

shows that throughout history, the minimum value of the road node density in the Changsha historic urban area has declined, meaning that the lowest level of connection between roads with the least connections in the historic urban area has continued to decline, supporting the argument that road planning in the context of a centralized government is conducive to improving the minimum utilization of roads in marginal areas. The minimum node density in 1914 was zero, showing that social changes and land expansion tend to produce abandoned roads, but the proportion was relatively low. The overall road system was found to be well connected with a low level of vulnerability.

3.2.2. Point of Contact Analysis in Various Periods

Table 2. Road Points of Contact in the Changsha Historic Urban Area in Various Periods.

	City Urban Roads in 1877	City Urban Roads in 1914	City Urban Roads in 1987	City Urban Roads in 2021
Numbers	0	1	0	0
Ratio	0	0.1%	0	0

shows that the only point of contact appeared in 1914. The absence of points of contact proves that, over time, road space evolution in the Changsha historic urban area has allowed the vulnerability of the road structure to remain low, empowering human–vehicle flow to circulate smoothly and avoid congestion. In 1914, the only point of contact occurred on Suburb Road 861, whose cancellation caused the isolation of its neighboring Road 862. However, this point of contact issue did not gravely affect the overall accessibility of the road structure. Considering that the location of the Changsha historic urban area has never been changed, it is concluded that the road layout in ancient Changsha is reasonable and its layout has been retained to the current day.

3.3. Comparative Analysis of Stability in Various Periods

3.3.1. Network Density Analysis in Various Periods

Table 3. Road Network Density in the Changsha Historic Urban Area in Various Periods.

	Urban Land in 1877	Urban Land in 1914	Urban Land in 1987	Urban Land in 2021
Network Density	0.21	0.04	0.09	0.06

shows that the network density was at its peak in 1877, and the density was relatively low in the other three time points investigated. Throughout history, the density has shown a downward trend, meaning that the road structure is the most stable in a centralized government system. Of the other three periods, the network density was lowest in 1914. An analysis of the historical background revealed that this was because the city developed and expanded outside of the city walls, thanks to the construction of the railway. The newly built roads were loosely connected to each other, and the road density in newly developed areas was too low. This also sheds some light on the fact that, in the initial stage of transport upgrading, the transformation in the ways that land-use information was disseminated had a splitting effect on the structural stability of the urban road network.

3.3.2. k-Core

Table 4. Road k-core in the Changsha Historic Urban Area in Various Periods.

Research Subject	No. of k-Core Zoning	Result and Value of k-Core Zoning	Ratio of 20-Core	k-Core Distribution
City Urban Roads in 1877	9	18K:2, 19K:1, 20K:2, 21K:67, 22K:45, 23K:2, 24K:89, 28K:29, 34K:35	99%
City Urban Roads in 1914	23	2K:2 3K:1, 4K:1, 5K:15, 6K:7, 7K:8, 8K:17, 9K:16, 10K:29, 11K:17, 12K: 42, 13K: 50, 14K: 48, 15K: 68, 16K: 56, 17K: 103, 18K: 206, 19K: 40, 20K: 11, 21K:50, 22K:68, 25K:26, 30K: 31	31%
City Urban Roads in 1987	9	5K:1, 13K:4, 14K:4, 15K:3, 16K:2, 17K: 49, 18K: 16, 19K: 41, 20K: 471	80%
City Urban Roads in 2021	22	5K:1, 7K:3, 8K:1, 9K:3, 11K:2, 13K: 7, 14K: 4, 15K: 9, 16K: 12, 17K: 26, 18K: 168, 19K: 18, 20K: 101, 21K: 113, 22K: 203, 23K: 35, 24K: 24, 25K: 40, 26K: 27, 28K: 28, 29K: 30, 36K: 37	72%

shows that, in general, the overall road network stability in the Changsha historic urban area has been decreasing throughout history. The K value was evenly spread in 1887, and the values accounted for a big proportion, meaning that the road network was the most stable. Of the other three periods, the K value was lowest in 1914 when there was an extremely polarized distribution. After checking the corresponding road serial numbers, it was discovered that the subcluster mainly included the roads in the newly developed area between the railway and the city wall, indicating that the low-density and distributed roads in the newly developed area had a reducing impact on the overall road accessibility. The K value increased in 1987 as a result of the after-crisis reconstruction that led to an upgrade of the road transportation facilities. The existing transportation conditions in the old urban area were consequently improved; however, the destruction brought by the crisis to smaller lanes and streets and the lack of newly built branch roads caused the overall stability of the road network to drop from the level in 1877. The K value was slightly lower in 2021 than in 1987, because some of the plots were adjusted in the marginal areas, and new roads were being constructed. The deeper reason behind such decrease is believed to be the prosperous development of the market economy, which resulted in accelerated land plot acquisition, leading to the gradual replacement of the original rich street texture of the historic urban area by orthogonal grids. As a result, the road network in the central area became more concise, whereas the development of non-key areas lagged behind. The parent–subsidiary pattern thus started to reappear as a side effect of the development of technology to reduce the tightness and stability of land accessibility. This also shows that the profit-driven model of the market economy is not conducive to the stable development of the overall urban road network and the protection of the spatial pattern.

3.4. Comparative Analysis of the Degree of Balance in Various Periods

Table 5. Statistics on the Degree of Central Potential in the Changsha Historic Urban City in Various Periods.

	City Urban Roads in 1877	City Urban Roads in 1914	City Urban Roads in 1987	City Urban Roads in 2021
Ratio of Degree Central Potential	1.87%	1.32%	1.85%	1.51%
Distribution of Degree Central Potential

shows that the general central potential peaked in 1877, with the other three target years showing lower results. This reflects that throughout history, the degree of balance in the road network in the Changsha historic urban area has been decreasing. The concentration of urban roads in 1877 was the most prominent, and the balance was the weakest. The centrality gradually increased in the three years of 1914, 1987, and 2021. Some scholars have concluded that, under the control of a centralized government, the historic urban area formed a single-center polarized urban space in 1877. This single-center structure was gradually changed by the end of feudal society to form a north-south dual center in 1914. In 1987, as the development projects in the historic urban area were reduced, the function of the historic urban area was restored to a single-center structure with administrative features. The centralization towards the historic urban area continued in 2021, as the agglomeration effect of the single-center commercial development was sustained [18]. Hence, it is concluded that political and economic changes led to changes in land use and centrality, influencing the degree of balance. The enhancement of the single-center development pattern in the historic urban area, when viewed as a function zone, is the main reason for the unbalanced development of urban roads.

3.5. Accessibility of Historic Sites

Tourism is conducive to the balanced development of the overall economy [28]. The land plots occupied by structures with conservation value are designated as land for cultural relics and historic sites. For relics and historic sites to fulfill their value, the accessibility of the land plots in which they are located must be prioritized: the greater the accessibility, the more willing the public will be to visit and the greater the possibility of making full use of the value of these sites will be. Therefore, the accessibility of historic sites and relics in the urban road network is represented by the centrality of the roads that connect to their land plots and the higher the former, the equally higher the latter, and consequently the more likely the conservation of culture is.

Table 6. Centrality of Construction Land Plots used for Relics and Historic Site Conservation in 2021.

Statistics Content	Statistical Results																					Location
No. of Plots	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	See Figure 5 for Exact Location
Conservation Level	Provincial	Provincial	Provincial	Provincial	Provincial	Provincial	Provincial	Provincial	Provincial	Provincial	National	National	National	National	Provincial	Provincial	Provincial	Provincial	Provincial	Provincial	Provincial
Average Centrality of Connecting Roads	57	44	24	46	44	27	41	38	54	60	61	75	15	51	32	52	77	28	43	45	26

shows that, in general, the overall centrality in the network in which the construction land plots used for cultural relics and historic site conservation is covered remains relatively balanced and was evaluated as being at a medium level evaluation. The space accessibility of the land plots is generally at an agreeable level. Given the need to protect the historic spatial layout and its impacts on the market economy, the accessibility of most of these plots should not be excessively altered. As there are five of them, based on their low utilization frequency and lower-than-30 centrality, it is suggested that improvements should be made.

The cultural relics and historic sites are integrated into the layout of the urban tourism system, and public transport and bicycle routes can be improved by the layout, promoting tourist activities in the city [6]. Meanwhile, the Changsha City Territorial Spatial Master Plan (2021–2035), published in 2021, indicates that the study area is part of the main city core area and the cluster of cultural innovation in the historic urban area. The Wuyi commercial area, which is the largest and most important business area in Changsha and the main service node for the city’s tourism, was also included in the study scope. Therefore, the combination of utilization routes of historical sites and the accessibility plan of the Wuyi commercial area is conducive to the protection and utilization of historical and cultural resources. As indicated in Figure 5, it is suggested that a tourism development axis should be included in Changsha’s urban tourism development plan to connect the entry and exit pathways to historical sites with the development centers. This development pattern would help to guide space-people flow, promote better use of historical and relic-related land plots, and increase the cultural diversity and economic value in the urban central area.

4. Discussion

4.1. Features of Road Accessibility in the Changsha Historic Urban Area

This study shows that the vulnerability of the road network in the Changsha historic urban area has been low and that not much has changed throughout history. In addition, stability has been decreasing while the degree of balance has been increasing. In a review of the road network structure in Shenzhen city, Wang Li concluded that the increase in the density of urban construction land is the main reason for the increase in traffic land density and nodes, and resources, environment protection, and eco-restrictions are the main reasons for the increase of complexity in, and decrease of, the structural stability of the road network [29]. Unlike Shenzhen, which is a new city, the research subject of this study is a historic urban area where, despite the change in focus of development planning to motor-car-oriented city building and the subsequent increase in newly built roads, the overall road density has still decreased compared to when walking was the major transport method. Additionally, resource protection, for example, through the construction of parks, green spaces, and historic sites, is one of the reasons for the decrease in road network stability. Shi Yaling used a network analysis to compare three historic areas in Chongqing and pointed out that the network stability changed with the structure of the network, meaning that a more compact network structure can lead to a more stable network relationship. Shi’s study also showed that geographical conditions and natural separation are the main reasons for the generation of vulnerability [30]. This paper shares some of Shi’s view while presenting its own unique findings. The evolution of the transportation structure in the Changsha historic urban area features a ‘down-up-down’ stability change, which is in line with the changing trend in the structure of the network. This finding echoes the view that the network layout is the main reason for changes in the stability of the land-use network. Nonetheless, the level of vulnerability has remained low in the Changsha case because the city was built on flatlands that generate less separation due to nature. Shi conducted a survey on routes in three parks and pointed out that geographical separation and scattered land use result in the formation of functional node network structure clusters, causing reduced stability and an increased degree of balance in the in-park node network [31]. In this study, a similar phenomenon was recorded but for different reasons. The main separation factors causing the formation of a parent–subsidiary pattern in the network were identified as the city wall and the shifting of key development areas due to changes in the times. The mainstream function change in the Changsha historic urban area was the ratio of land used for public service and administration, resulting in an ‘up-down’ trend in the degree of balance in the network structure. This is also consistent with the finding that the function of construction land in the Changsha historic urban area evolved from a single-center development to a development of multiple centers and then to a single-center development [18]. It is, therefore, concluded that the decentralized layout of central nodes is conducive to the improvement of the degree of balance of the road network.

4.2. Major Obstacles to Improving the Road Accessibility of the Changsha Historic Urban Area

This paper shows that vulnerability in the Changsha historic urban area has always been very low. There has been no threat caused by vulnerability in its network structure with the exception of the occurrence of destructive disasters. The evolution of road accessibility is mainly reflected in the stability and degree of balance in the area. In the development of road accessibility in the historic urban area, the stability and degree of balance of the road network have also been affected by the distribution of the central area, while functional zoning has been affected by three main factors: the era background, the economy, and the conflict between conservation and development. In discussing the development of the accessibility of urban roads in the Changsha historic urban area, we suggest that the disappearance of the capillary road caused by urban renewal during the rapid urbanization process and the consequent decrease of road density are the main factors affecting road accessibility in the Changsha historic urban area, because land use in the historic urban area has undergone dynamic adjustment, the city wall and the railway, which were considered to be earlier separation factors, have already ceased to exist, and there are no natural environmental barriers in the area. The uneven development of the central and non-central areas will be further polarized by capital in the market economy. Therefore, the unsustainable single-center development trend is the main obstacle to the maintenance of the stability and degree of balance of the road structure in the Changsha historic urban area. The Changsha historic urban area is still an important central area to the city. Old city renovation projects, such as building large commercial complexes, will inevitably cause a large number of immovable cultural relics to disappear and lead to the demolishment of historic streets [18]. This problem is further catalyzed by the market economy, which helps the historic urban area maintain its status as the commercial center of the city. Consequently, transportation stress in the city becomes more unbalanced, and the conflict between space and function, which is also a key problem in terms of the conservation of historical and cultural heritage, remains unsolved. Therefore, we suggest that, to conserve and develop the Changsha historic urban area, it is important to optimize transportation accessibility in the historic urban area, protect the spatial layout in the historic urban area, adopt a multiple nuclei model strategy from the urban planning level, and enhance transportation accessibility for relics and historical sites.

4.3. Suggestions for Road Accessibility Optimization in the Changsha Historic Urban Area

In developing the accessibility of the Changsha historic urban area, equal emphasis should be given to stability and the degree of balance. In terms of promoting the stability of the urban road network, network dynamic stability tests could be introduced to identify relatively more important internal connection channels and roads with lower levels of connectedness. Improvements can be made from the two aspects of planning and management to increase the stability of the urban road network while simultaneously analyzing the features of the network structure and the functions of the lands in question. The ratio of public service facilities, parks, and green spaces can be increased to further enhance the stability of the urban road network. In terms of promoting the structural balance of the urban road network, effort can be made to improve the nodes that currently have a lower degree of central potential in the network and plan more centers in urban functions. It is recognized that continued respect for history is highly valuable for the city’s development. However, the centrality of roads connected to relics and historic sites in the Changsha historic urban area is generally low. Hence, this paper suggests that the degree of centrality of the roads leading to the main entrances of such sites should be improved as a measure to enhance their accessibility. Road optimization is usually achieved by enhancing the hierarchy of the network, for example, by building small roads to add shortcuts and constructing transport hubs of various levels to enhance the connection between centers and from the center to the outskirts of the city [32]. In historic urban areas, it is necessary to protect the spatial layout that is of historical significance, and architecture functions can be converted to meet the needs of urban use [33]. To realize this, a complex network analysis should be implemented to assign levels to roads in the city and develop comprehensive improvement measures for historic and non-historic areas, according to the indicators. The structural importance of the roads in the area, their levels, and the accessibility of the planned road network can also be determined [34]. For instance, intermediate grids can be added between the outer road network of the historic conservation area and the internal tree grid to reconcile the contradiction between microeconomic movement and the increase in historical and cultural utilization. In terms of freight distribution, factors such as the ability to continuously develop and adapt to a dynamic environment, logistics and supply chain management competence, and the ability to take full advantage of advanced IT are taken into consideration [34,35], as well as optimizing the logistics system to avoid energy waste and promoting low-energy consumption transport [36]. The adoption of IT technologies to control traffic use at different times in historical urban areas is recommended, for example, adapting to the development of the service industry and commuting needs during the daytime and material supply and urban cleaning during the nighttime.

5. Conclusions

The vulnerability of the urban road network in the Changsha historic urban has always been low, and the evolution of road accessibility is mainly reflected in the stability and degree of balance of the network structure. Specifically, the stability has shown a downward trend, and the degree of balance has shown an upward trend. The stability of the urban road network is mainly affected by the network layout, which is mainly determined by how the roads connect with each other. The city of Changsha is built on a plain and has few natural barriers. The main factor affecting road connection is, therefore, artificial changes brought about by development. In earlier stages, this was represented by the city wall and railway. Now, it is the road network density changes brought about by urban renewal originating from resource protection and rapid urbanization. The degree of balance in the road network is mainly affected by the functional zoning of the construction land in the historic urban area. The control of capital under the market economy is the main reason for the unbalanced land value and the strengthened development of the single center. It is also the main obstacle to the conservation of historical and cultural heritage. Therefore, we believe that active and dynamic monitoring of the network structure in the Changsha historic urban area should be introduced to identify important connection channels. This could lead to the development of improvement projects to enhance the stability of the network structure, increase the key node degree central potential, and facilitate functional zoning so that the degree of balance of the network structure can also be elevated. The monitoring results may equally promote the leveling of roads to create a separate level-based improvement measure for road governance in designated historic and non-historic areas to improve accessibility to relics and historic sites and promote their utilization. This may be obtained by optimizing the logistics system to avoid energy waste and promoting low-energy consumption transport means. Macro guidance can be given based on higher-level planning. The development of urban tourism routes, including the connection of land plots containing cultural relics with key nodes, such as the Wuyi commercial area, to guide space-human flow and increase the diversity of tourism attractions in historic urban areas and the protection of such relic sites, is of huge significance to the protection and development of the Changsha historic urban area. At the same time, this methodology is also applicable to cultural and tourism cities of other types, as it can help local stakeholders and decision makers to understand the relationship between transport accessibility and key space nodes and can aid in the development of introductory development strategies.