Impacts of Nanchang Metro on Accessibility of Public Transport Network and Fairn

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1. College of City Construction, Jiangxi Normal University, Nanchang 330022, China; 2. School of Urban Construction & Safety Engineering, Shanghai Institute of Technology, Shanghai 201418, China

Abstract Based on the GIS spatial analysis technology, this paper assessed the effects of Nanchang metro in improving the accessibility of public transport networks in different spatial patterns. Besides, from the perspective of transport fairness, this paper evaluated the fairness of allocation of transportation resources for indemnificatory housing residents. Then, it revealed the reasons for the welfare loss of indemnificatory housing residents in fast rail transit resources, so as to provide a reference for promoting the space adaptation of indemnificatory housing residents. The study found that (i) the subway has improved the accessibility of the urban public transport network in terms of travel time and accessibility, but it has a different effect on improving the accessibility of the public transport network. After crossing a certain transit time and distance, there is a weakening trend, showing a pattern of "central expansion-peripheral weakness". (ii) The relative improvement of the metro on the accessibility of public transport for indemnificatory housing residents is lower than the overall improvement efficiency, and the fairness of the redistribution of transportation resources of the indemnificatory housing residents is impaired. (iii) In order to prevent and reduce the problem of space mismatch between indemnificatory housing and rail transit, it can be achieved by planning the metro network according to the spatial characteristics of indemnificatory housing residents’ activities, guiding the selection of sites for indemnificatory housing with the TOD model, and forming a mixed community by combining the indemnificatory housing construction with commercial housing, to guarantee fair resource allocation of indemnificatory housing residents.

Key words Nanchang Metro, Accessibility, Indemnificatory housing residents, Fairness of transport

1 Introduction

Indemnificatory housing is house provided by the government for low-income residents with limited standards and at limited price or rental. The spatial distribution of indemnificatory housing in the city determines the spatial location and concentration of low-income and middle-income groups living in the city. Although it solves the housing problem of low-income residents, due to the passive nature and spatial distribution, the residents are faced with social and transportation problems such as spatial dislocation, high travel costs, and poor accessibility[1-2]. Some scholars believe that high transportation expenditures, long travel time, insufficient public transport facilities, and incomplete transport network will exacerbate poverty in low-income groups[3-4]. Therefore, the improvement of urban public transport planning and the scientific selection of indemnificatory housing complement each other, both of which are the main factors that guarantee the travel fairness of residents.

As public welfare infrastructure, rail transit is a special public resource. Its planning goals should be changed from pursuing the overall efficiency goal of "homogeneous population, uniform results" to structural equity goals that take into account "different groups, different outcomes", advocate for the promotion of vertical equity, emphasize the concern of the spatial distribution of public transport facilities for the benefit of social vulnerable groups. Many scholars abroad have undertaken extensive studies on the travel accessibility and transportation equity of low-income people. The first type of research is based on the unfair transportation of space mismatch. Low-income jobs are more spatially distributed than professional high-income jobs. Low-income people are concentrated in urban areas with fewer job opportunities, which separates the work and residence, forming a vicious circle of low-income work places, low-income groups, and low mobility[5-9]. The second type of research is based on the unfairness of the traffic structure of different groups. The National Family Travel Survey conducted by Canada in 2001 showed that approximately 78% of public transport and light rail trips occurred in households with an annual income of less than 40 000 USD, and only 13% of these income groups were rail commuters, and most people use cheaper public transport to travel[6-8]. The third type of research is based on the unfair comparison between the past and the present. The analysis of Montreal’s transportation planning in Canada shows that the potential effect of strong neighborhoods obtained from traffic planning increases more than that of weaker neighborhoods, leading to an increase in the future unfair gap[10-11]. In contrast, related research in China has just begun, and it mainly focuses on the analysis of public transport travel difference between residents[12-17], the accessibility changes of low-income people[4,18-22], site selection of indemnificatory housing and occupational-living space mismatch[1,3,23], and has achieved fruitful research results. In the context of rapid development of rail transit, some scholars have proposed a new pattern of regional occupational-living imbalances in the context of the development of rail transit network based on rail transit research on the changes in occupational-living space. Rail transit has accelerated the suburbanization of the residential population and aggravated regional occupational-living imbalance. Besides, some scholars investigated the location of indemnificatory housing around rail transit stations[24-27]. However, the effects of rail transit on different cities, different spaces, and different social classes are different. The domestic literature mainly studies the more developed cities such as Beijing, Shanghai and Guangzhou. There are few studies on the accessibility of Nanchang Metro, and the related research on the impact of Nanchang Metro on social equity is basically blank. In view of this situation, taking Line 1 and Line 2 of Nanchang Metro as examples, we studied the impacts of rail transit on accessibility of public transport network and fairness of travel for indemnificatory housing residents.

In the context of the emphasis on "transportation fairness" and the current widening income gap between different social classes, the formulation of indemnificatory housing and public transport policies faces a series of challenges. It is urgent to clarify the improvement benefits of rail transit for indemnificatory housing residents, to formulate targeted improvement measures and gradually eliminate the unfair starting point and unfair redistribution in resource allocation. Taking main areas of Nanchang City as examples, based on the public transport, we evaluated the accessibility of rail transit, analyzed the improvement effects of rail transit on the accessibility of different spatial patterns, and discussed the differentiation of rail transit for travel of residents. There are three points of innovation. (i) In view of the difficulty in obtaining public transport network data, the OpenStreetMap open data platform was used to obtain the vector data needed to measure the accessibility of public transport. Based on GIS spatial analysis technology, a composite public transportation network model was established, which is helpful for simulating residents’ travel. Thus, there is some innovation in data acquisition and use. (ii) A large number of travel units was used as the basic measurement unit, so measurement results are relatively accurate. (iii) From the perspective of transport fairness, we evaluated the fairness of allocation of transportation resources for indemnificatory housing residents, revealed the reasons for the welfare loss of indemnificatory housing residents in fast rail transit resources, so as to provide a reference for promoting the space adaptation of indemnificatory housing residents.

2 Data source and study method

2.1StudyareaanddatasourceInthispaper,wetookNanchang City’s main urban area loop expressway and south outer ring expressway as the research area, covering an area of 1 017 km2, involving the entire Qingyunpu District, Xihu District, Donghu District, and Qingshanhu District, Wanli District, Xinjian District and Nanchang County. Travel means include buses, subway and walking. The research data include travel unit, bus lines and stations, subway network, and distribution of indemnificatory housing.

Transport network data. In 2016, the city bus lines, stations and pedestrian lines were used as the network form before the opening of the subway, and the city bus lines and stations, subway lines and stops, and the pedestrian line in 2018 represented the network form after the subway was opened. The study area transport network vector data were selected from the OpenStreetMap website.

Travel unit. We divided the travel unit into 5 416 units according to the district administration, road network shape, and land nature. The administrative affiliation and land use nature of the parcels within the unit are consistent.

Indemnificatory housing distribution data. The data of indemnificatory housing distribution were selected from MetroDataTech platform.

2.3Researchindicatorsandtechnicalmethods

2.3.1Building of public transport network model. At present, the methods widely applied in traffic accessibility are mainly based on transport network datasets. The transport network model has clear geographic coordinates and is close to the actual road network structure. The efficient coordination and connection of composite transport networks is the foundation of the maximum effectiveness of the entire public transport system[28]. With the aid of the GIS network analysis tool, we built a public transport network model with the bus-walking network structure as the public transport network model before the subway opening, using the bus-subway-walking to represent the public transport network dataset after the subway opening. Network travel costs were measured in terms of time distance. The walking network and subway travel network speeds were set at 5 and 50 km/h, respectively. The public transport network classifies the travel speed according to urban road grades and average speeds of Nanchang buses. The city’s main and secondary roads and streets were set at the speed of 20, 15 and 10 km/h. Taking the geometric centroid of the travel unit as the starting point and destination point, we selected commercial service centers and employment centers such as Bayi Square, Zhongshan Road Rainbow Store, Dream Times, Honggu Bund Wanda, transfer centers such as Nanchang Station and Nanchang West Station, medical care service centers such as First Affiliated Hospital and Second Affiliated Hospital, and Qiushui Square and Yaohu Forest Park.

2.3.2Methods for measuring public transport accessibility. Space distance, time distance, economic distance, and network development are usually used as basic factors to measure the accessibility. The accessibility measurement methods based on topological networks mainly include the shortest distance model method, cumulative opportunity method, isochronous circle area method, gravity model method, and network connectivity index method,etc.[29-33]. Based on the analysis of demands, we used the shortest weighted average travel time distanceTiandODcost matrix used to measure the time distance. And according to the isochronous circle, we analyzed the impact range of the public transport network. We used the accessibility coefficientAito calculate the connection level of the transport network.

The weighted average travel time indicator is a measure of the time from one node to another. The lower the indicator score, the higher the accessibility of the node, andviceversa. This model is widely applied in traffic accessibility studies. The formula is as follows:

TheODcost matrix is an important indicator for measuring the degree of connectivity between nodes. The formula of the matrixLformed by the shortest time distance is as follows:

(1)

whereTidenotes the accessibility of nodei,Tijdenotes the shortest time distance from nodeito nodej,Mijdenotes the driving cost weight of the road section from nodeito nodej, andnis the number of nodes in the study area.

L=[lij]n×n

(2)

The accessibility coefficientAireflects the relative accessibility level of each node in the transport network. The formula is as follows:

(3)

where the accessibility coefficientAiis the ratio of the total time distance of each node to the average value of the total time distance of the nodes in the area,nis the number of nodes,Tijis the sum of the shortest time costs of nodeitoj, andTrepresents the sum of the shortest time costs among all nodes. The smaller the accessibility coefficient, the better the accessibility. WhenAi>1, the accessibility of nodeiis lower than the overall accessibility; whenAi<1, it indicates that the accessibility of nodeiis better than the overall accessibility.

3 Method realization and results analysis

3.1Analysisofsubwayaccessibilitytopublictransportnetworkbasedonmicro-travelunitscale

3.1.1The overall impact of the subway on the accessibility of the travel unit. Based on the public transport network model, we calculated the shortest time cost of each travel unit to all public service centers, nearest commercial service centers, all external transportation centers, nearest external transportation centers, and travel units before and after opening of subway. According to Table 1, before the opening of subway, the average time cost of travel unit residents to all public service centers was 84 min, and the average time costs to the nearest commercial service center and external transportation transfer center were 58 and 68 min, respectively. In addition, the average time distance between travel units is 110 min. After the opening of subway, the shortest time distance for residents to travel has been significantly reduced. The time to all public service centers has been shortened to 59 min, which is 25 min less than before the opening of subway, and the time cost has been improved by 30%. The average time cost of residents to the nearest commercial service centers and external transportation transfer centers decreased by 12 and 13 min, and improved by 21% and 20%, respectively. It can be found that the accessibility of the subway to the travel unit has been significantly improved.

Table1EffectsofNanchangMetroonaccessibilityofpublictransportnetworkbasedonnetworkanalysis

Public transport networkTotal costfor goingto all publicservicecentersAverage costfor going toall publicservicecentersTotal cost forgoing to thenearestcommercialservice centersAverage costfor going tothe nearestcommercialservice centersTotal cost forgoing to allexternaltransportationtransfer centersAverage costfor going toall externaltransportationtransfer centersTotal cost forgoing to thenearest externaltransportationcenters centersAverage costfor going to thenearest externaltransportationtransfer centersODmatrixtimecostAveragecostfor travelbetweentravel unitsBefore the subway opening456 81084313 87658532 34898370 65368596 647110After the subway opening319 27359248 39946343 91864297 56655477 12988Improvement137 5372565 47712188 4303473 08713119 51822

3.1.2Improvement of subway accessibility services in different time ranges. Using the cumulative area method, starting from the selected 10 typical public service centers, we measured the impact of the subway on the service area level of all facilities. Setting the impedance time interruption value at 10 min, can be found that the service area of public service facilities has been increasing with the continuation of time (Fig.1 and Fig.2). Before the opening of subway, the accessible areas of the service area travel time of 10, 30 and 60 min separately accounted for 1%, 12% and 42% of the total area of the study area. After the subway opening, the service area within the travel time of 10, 30 and 60 min increased to 2%, 18% and 50%. To public service facility points within the travel time of 40 min, both the absolute and relative accessibility have been constantly improving. When the travel time reached 40 min, the improvement of subway to service area accessibility reached the peak value. However, beyond the 40 min of travel time, although the absolute accessibility has been improved, the relatively accessibility showed unstable fluctuation and weakening trend, indicating that the improvement of subway to service area accessibility is not always increasing, instead it will decline after reaching a certain travel time.

3.1.3"Central expansion-peripheral weakness" rules in the spatial pattern of subway accessibility. In order to further reveal the accessibility improvement effect of Nanchang subway in different spatial patterns, using 0.5 km interval scale as buffer zone around subway stations, we calculated the traffic accessibility coefficient Ai from the travel unit to the destination on the buffer zone before and after opening of subway, and made an in-depth analysis of its relative accessibility rules (Fig.3). The results show that the accessibility coefficient after the opening of subway was greater than 1 outside the station buffer zone with a threshold of 3.0 km. At this time, the accessibility of each node on the buffer zone was lower than the overall accessibility of the transport network, and the value of the accessibility coefficient before the opening of subway was less than that after the opening of subway, indicating that the relative accessibility of the subway has decreased; within the threshold of 3.0 km station buffer zone, the subway would be helpful for improving the absolute and relative accessibility of the public transport network, and its accessibility would be better than the overall accessibility. This indicates that the improvement of subway to traffic accessibility of Nanchang main city area is different, and the spatial pattern of accessibility shows the "central expansion-peripheral weakness" rules.

Note: a. Public transport network accessibility of service areas before opening of subway; b. Public transport network accessibility of service areas af-ter opening of subway.Fig.1 Impacts of opening of Nanchang Metro on public traffic ac-cessibility based on cumulative area methodFig.2 Improvement of subway accessibility services in different time ran-ges

Note: a. To commercial service center; b. To external transportation transfer center; c.To medical care service center; d.To parks and squares; e.To all public service centers.

Fig.3Differentimpactsofsubwayopeningonimprovementofaccessibilitypattern

3.2Analysisoftheimpactofsubwayonpublictransporttravelaccessibilityofindemnificatoryhousingresidents

3.2.1Spatial distribution of indemnificatory housing. With the help of Arcgis nuclear density analysis tool, we analyzed the spatial distribution density of indemnificatory housing and calculated the density in the surrounding neighborhood, as shown in Fig.4. The darker the color, the higher the degree of indemnificatory housing concentration. It can be seen that the indemnificatory housing is mainly distributed in the south and east of the city, and it is mainly between the second and third rings, and most are resettlement housing. The indemnificatory housing along Chengnan Avenue and Changnan Avenue expressway showed significant concentration, and the remaining were scattered in space. The construction of indemnificatory housing was mainly centralized construction, and indemnificatory housing built in a centralized manner was scattered in the distribution density. Two-thirds of the indemnificatory housing were 3 km beyond the stations, and the subway has caused a loss of the relative accessibility of residents (Fig.5).

Fig.4Spatialdensityofindemnificatoryhousing

Fig.5Distributionofindemnificatoryhousingwithin3kmrangeofstations

3.2.2Improvement of subway to public transport travel accessibility of indemnificatory housing residents. Based on the concept of social justice, the construction of the subway should be beneficial to social vulnerable groups. In order to further reveal the positive and negative effects of the subway on the accessibility of public transport travel for indemnificatory housing residents, we took the indemnificatory housing and all travel units as the starting point, and took 10 typical public service centers as the destination, compared the improvement efficiency of the subway to public transport travel for residents of indemnificatory housing and all travel units. As shown in Table 2, the subway can reduce the time cost of indemnificatory housing residents, and the improvement efficiency was 26.47%, but it was still not as good as the overall improvement ratio of subway (34.69%). In addition, as shown in Fig.6 and Fig.7, the improvement of subway to travel range of indemnificatory housing residents was always lower than 2.5%, while the average improvement of the subway to overall travel range was up to 5.2%, indicating that the improvement of subway to public traffic travel of indemnificatory housing residents was lower than the overall improvement effect, and it exerted a negative effect on the indemnified objects in enjoying and having fair transportation resources, made the indemnificatory housing residents fall into the welfare loss and aggravated the unfairness of reallocation.

Fig.6 Comparison of the improvement of subway to travel accessibility of residents of indem-nificatory housing and all travel units within different time rangesNote: a. Accessible range of public transport for indemnificatory housing residents before the opening of subway; b. Accessible range of public transport for indemnificatory housing residents after the opening of subway.Fig.7 Comparison of the accessible range of public transport for indemnificatory hous-ing residents before and after the opening of subway

Table2Impactsofsubwaytopublictransporttravelofresidentsofindemnificatoryhousingandalltravelunitsmin

Public transport networkIndemnificatory housingTotal cost for going to all publicservice centersAverage cost for going to allpublic service centersAll travel unitsTotal cost for going to all publicservice centersAverage cost for going to allpublic service centersBefore the subway opening41 74682532 34898After the subway opening30 69660343 91864Improvement cost11 05022188 43034Improvement efficiency∥%26.4726.8335.4034.69

3.2.3Factors that influences subway aggravating the unfair redistribution of indemnificatory housing residents Transport fairness is a basic requirement of social fairness, so public resources should be inclined to vulnerable groups. In order to alleviate the unfair distribution of Nanchang Metro for public transport travel of indemnificatory housing residents, it is necessary to take account of the subway line network planning, site selection and construction methods of indemnificatory housing. (i) In the planning of the subway line network, the model should be based on factors such as city function, nature, shape, and land use to optimize the plan, but also consider the low-income groups of indemnificatory housing, balance social and economic benefits, and really care about the vulnerable groups. (ii) At present, indemnificatory housing of Nanchang City is mainly located in a marginalized area with poor transport network and incomplete supporting facilities. Most of indemnificatory housing residents cannot pay for private cars and have a strong dependence on public transportation. Therefore, it is required to attach greater importance to the convenience of transportation of in the site selection of indemnificatory housing. With the development of social economy, the opportunity cost of labor time is increasing. If indemnificatory housing is kept away from fast transit, it will not only increase the relative travel cost of residents, but also reduce their income. Therefore, it is important to reasonably ensure the spatial relationship between the housing location and the subway. Based on this, the rail transit-oriented TOD model can be combined with the site selection of indemnificatory housing. Taking the construction of the indemnificatory housing subway community in Xiamen as an example, a group of indemnificatory housing can be planned and constructed in a high-quality area near the rail transit station outside the island. The main community of the indemnificatory housing subway community should consider the connection of subway stations, indemnificatory housing, public services and life support projects, coordinate the promotion of the ground and underground, and improve the travel accessibility, sense of gain and happiness of indemnificatory housing residents. (iii) Land resources in the old city area are limited and the land price is high, so they are generally not considered as the first choice for the development of indemnificatory housing. The construction method of indemnificatory housing in Nanchang is mainly focused on the construction in new districts, which will easily aggravate the disadvantaged position of indemnificatory housing, thereby weakening the public transport accessibility of indemnificatory housing residents. The endowed location conditions of the old city are urgently needed by low-income and middle-income people. In the site selection of indemnificatory housing, the opportunity of the transformation of the old city and the adjustment of the urban structure in the process of urbanization can be used to mix construction of commercial housing with indemnificatory housing using the "large mixed living and small centralized living", to make indemnificatory housing residents enjoy the positive benefits brought by resource allocation of the rapid rail transit.

4 Conclusions and discussions

Based on the GIS spatial analysis technology, we evaluated the impacts of Nanchang metro on improving the accessibility of public transport networks in different spatial patterns. Besides, from the perspective of transport fairness, we analyzed the effects of subway in improving travel of indemnificatory housing residents, and further revealed the reasons for the welfare loss of indemnificatory housing residents in fast rail transit resources. We found that: (i) The subway has improved the accessibility of the urban public transport network in terms of travel time and accessibility. (ii) The subway has a different effect on improving the accessibility of the public transport network. After crossing a certain transit time and distance, there is a weakening trend, showing a pattern of "central expansion-peripheral weakness".

The subway can improve the accessibility of public transport travel of indemnificatory housing residents, but the level of redistribution of fast rail transit resources for the residents is lower than the overall level, and its basic traffic accessibility lacks guarantee.

Both indemnificatory housing and urban rail transit are at a rapid development stage, and their spatial distribution is dislocated, which is not favorable for the fair improvement of the travel accessibility of the indemnified residents. To prevent and reduce such resource mismatch problems, we came up with following recommendations. (i) In the planning of the subway line network, it is recommended to take into account the space characteristics of the activities of the indemnificatory housing residents, especially the employment space of those residents, to alleviate the mismatch of travel space as much as possible. (ii) In the site selection of indemnificatory housing, it is recommended to guide the location of the indemnificatory housing combined with the TOD model. For the relatively remote stations in the first and last sections of the subway or in the middle, "string-of-bead" mixed development can be adopted. For areas along the subway or both ends, it is recommended to develop indemnificatory housing within the reasonable walking time to stations. At the same time of considering land price and travel convenience, it is necessary to reduce the travel time cost and transport cost of indemnified objects. (iii) In the construction of indemnificatory housing, it is recommended to construct indemnificatory housing in combination with commercial houses, to form mixed communities, guarantee location centralization and distribution decentralization of indemnificatory housing, to realize balanced allocation of resources.