| Urban public facilities are closely related to the daily activities of inhabitants,which affect residential survival,development,well-being and health,such as education,health,culture,sports,transport,social welfare and security.Spatial accessibility has been widely used to evaluate the rationality of the spatial distribution of public facilities.It can not only reflect the convenient degree of population access to public services through the transportation networks.Moreover,it can better reveal the unevenly distribution of public facilities and resources allocation.Therefore,reasonable and effective accessibility methods of public facilities are of great significance for the development of spatial equity theory,the achievement of the goal of 'equalization of basic public services' and sustainable socioeconomic development.At present,the accessibility methods of public facilities have been greatly improved compared with previous studies at home and abroad.However,most studies only evaluate the spatial accessibility,but the accessibility is not only subjected geographical restriction,but also suffers from temporal constrains.As inseparable linkage between temporal and spatial components,accessibility should study in the context of spatio-temporal geography.However,most accessibility methods are achieved based on statistic road network datasets,ignoring the impact of road network connectivity,traffic congestion and transportation modes.Hence,there is a deviation that public service related planning and decisions based on simplistic accessibility measures might cause unwanted outcomes.In addition,the existing research scales has been mainly concentrated on the census administrative street and traffic analysis zones,lacking an analysis at the individual level(population—the object of public services).With the rapid development of geographic information technology(GIS),transportation,space awareness and mobile technology,open geo-big data of Located based services(LBS)are closely related to national economy,social development and daily life.It meets the needs of residents'travel while its back-end server system has also accumulated a large amount of detailed micro-data,which have distinct spatial and temporal characteristics,and provides a new data source for in-depth study of the spatio-temporal accessibility of public facilities.Therefore,the traditional methods based on physical accessibility need to be further changed,and the method of spatio-temporal accessibility has more important theoretical significance and application values for the spatial layout and optimization of public facilities.This paper firstly reviews the concepts,principles,methods,application and limitations of accessibility in previous studies.Then,takes Nanjing,a highly urbanized city,as our case study,and integrates mobility(transportation modes)and temporality to measure the pattern of distribution and difference characteristics of spatio-temporal accessibility to public facilities.The main contents of this paper and related research conclusions are described as follows:(1)Measuring temporal accessibility in multi-mode transportation networks.Accessibility analysis is recognized as an efficient way to assess interactions between transportation and land use.Travel times form an essential part of such as an analysis.In the past,distance-based accessibility often used Euclidean distance,Network distance or Raster cost distance.The Euclidean distance is inconsistent with the actual transportation environments.The Network distance considers the perfection of the road networks,but not considering the classes of road networks.The Raster cost distance consider the classes of transportation networks,but it assumes that all road networks are open.The few exiting studies considered the connectivity of road network,traffic congestion informations and transportation modes when people seek public services.The paper applied the so-called 'door-to-door' approach to build a unified conceptual model for multimodal O-D travel times,and uses the Navigation Path Direction API(Application Programming Interface)based on WMS(Web Map Service)and dynamic traffic information provided by map developer to harvest more realistic and comparable results.Then,the four basic temporal accessibility metrics are developed to measure the temporal accessibility of various public facilities via different travel modes(walking,riding,public transport(PT)and private car).These metrics not only describe the‘closest'proximity to‘local'public facility,but also provide comprehensive information for the cumulative accessibility opportunity to the 'global' public facilities.At the same time,in order to reflect the disparities between the mobility for transportation modes,this paper also proposes a modal temporal accessibility gap indicator,which is used to assess the car dependency.Conclusions can be drawn as follows:?The estimation of travel time via map Direction API,considering the traffic congestions,intersection delays,searching for parking places,transfer time,waiting time,and walking is more objective than the traditional GIS-based vector network or raster cost analysis.The analyses are based on open access data and publicly available open-source tools,and thus similar analyses can be conducted in urban regions nationwide.Moreover,the huge workload of building and updating of transportation networks can be avoided,to some extent,the accuracy and reliability of the accessibility calculation can be improved;?The travel mode has a prominent impact on the outcome of the analysis of accessibility.When analyzed in a comparable manner,private car can be an even faster than other travel modes to access public facilities,but it is affected by road congestion and finding parking places;?The spatial distribution of the modal temporal accessibility gap between the private car and the public transport(PT)has obvious expanded along the PT routes.The 'spatio-temporal compression effect' produced by the metro is particularly evident.(2)Measuring spatio-temporal accessibility of public facilities supported by the isochronous traffic circle model.Accessibility is an important indicator of the location advantage.Taking Nanjing's commercial center as an example,an'Isochronous Traffic Circle' tool is developed based on Derication API,and with the aid of GIS software to measure and evaluate the spatio-temporal accessibility distribution pattern,temporal changes and its spatial location advantages characteristics of various commercial centers among car,bus,metro,and riding modes.At the same time,taking into account the competitive relationship of facilities,integrating the nearest facility and accumulated opportunity method,the spatio-temporal accessibility of the commercial centers is measured,and the results can not only reflect the service level of the 'supply side' facilities and transportation,but identify the areas where the facilities can not serve within the specified time threshold.Conclusions can be drawn as follows:?Compared with the traditional physical accessibility measurement,the spatio-temporal accessibility measure based on WMS is more accurate,convenient and efficient.It can be achieved in a variety way of multiple transportation modes for spatio-temporal modeling,analysis and expression;?The accessibility of commercial centers show the‘core-periphery'regional differentiation characteristics.The commercial centers of the central urban have good accessibility by PT,and its spatial distribution shows the characteristics expanded along the metro lines and bus lines;The commercial centers of the marginal area has better accessibility by car,and its spatial distribution shows the characteristics of expanding along the external traffic routes;The accessibility of the commercial centers both riding or walking modes is not much different,and the range of spatial accessibility for each commercial center shows the characteristics of the 'buffer' expansion,but influenced by the barrier of Yangtze River,the direction and rapid rate of expansion of the accessibility are limited;?Due to the influence of the real-time 'traffic flow' impedance factor of urban road networks,the accessibility of commercial centers fluctuates at different times of the day,and the range of accessibility of each commercial center decreased significantly at peak hours;?The measurement of traffic location of the commercial centers shows that improving the performance of public transportation services can effectively reduce the dependence on car.(4)The spatio-temporal accessibility measure of supply-demand matching based on the extended 2SFCA model.Taking into account the effects of temporality and modality when residents seek public resources services.Based on the two-step floating catchment accessility method(2SFCA)and spatialized population data,the paper proposes an innovative spatio-temporal two-step floating catchment accessibility method(Spatio-temporal 2SFC A)for measuring accessibility of populations to the high level hospitals.Due to the integration of road traffic conditions,the supply catchment and the demand catchment are no longer fixed as the traditional 2SFCA model,but vary with the time fluctuation,and both the level of service of the facility and the ability of individuals to acquire resources during the day time is accompanied by traffic flow.Then,taking Nanjing's high level hospitals as case,the spatio-temporal accessibility of general hospital resources is calculated under different travel modes and multiple time thresholds.Conclusions can be drawn as follows:?Spatio-temporal 2SFCA can provide a more accurate and realistic measure of the interaction between residents and public facilities.Spatio-temporal analysis for the variations of accessibility can provide quantitative and accurate evidence for geographically local and dynamic strategies of allocation decision-making of medical resources and optimizing health-care systems.It provides a scientific reference for spatial layout optimization and dynamic resource allocation services for other public facilities or cities;?The characteristics of time variation are significant,the proportions of residential areas with good medical accessibility are in the order of night,noon,afternoon,early morning peak and late evening peak from high to low;?There is a significant correlation between the accessibility values of resource services at each period.In general,grid cells with higher accessibilities at a time period are likely to also have higher accessibilities in other time periods,and vice versa.(5)Application of spatio-temporal accessibility method of public facilities with multi-mode transportation networks.Takes the Nanjing's general hospitals as a case,the spatio-temporal accessibility methods in the paper is comprehensively utilized to evaluate and analyze the spatial distribution of temporal accessibility and supply-demand capabilities of public facilities.Taking into account the differences in mobility among multiple population groups,a Multi-mode 2SFCA method integrated with multiple transportation modes is developed to measure the spatial accessibility of medical resource,and then,to identify resource oversupply,matching,and insufficient areas.Through the calculation,comparison and analysis of accessibility,it is found that:?The results of spatio-temporal accessibility measures take into account the mobility of population,having wider application prospects,especially in cities where the transportation is rich;?In terms of the temporal accessibility analysis,it can be seen that the travel times via car has increased due to traffic congestion,and the degree of increasing is different at each time periods of the day;?Sensitivity analysis shows that as the impedance coefficient ? increases,the spatial accessibility differentiation of population to medical facilities becomes larger,especially at peak time periods;The areas of highly gathered hospitals and road network dense have better accessibility,and vice versa;?The proposed innovative multi-mode 2SFCA incorporating both public and private transport modes yields separate accessibility scores for each modal group at each demand point to better reflect the accessibility levels.Moreover,this study discovers that the multi-mode PT users are disadvantaged in the competition for medical services with the multi-mode car users.The lack of public transportation services is the main reason of the uneven distributions of medical reasoures accessibility in Nanjing;?The multi-mode car users,the multi-mode PT users and the multi-mode users have similar spatial distribution of accessibility,which is represented by the main urban area and Jiangning district as the high accessibility scores,and the surrounding and marginal area showing low accessibility scores due to a lack of high level medical resources.More healthcare resource should be allocated and the public transport to hospitals should be improved in the peripheral areas.The proposed model can also be applied in other scenarios considering multiple population groups with different demand intensity for public services and mobility. |
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