A K-nearest neighbor （K-NN） based nonparametric regression model was proposed to predict travel speed for Beijing expressway. By using the historical traffic data collected from the detectors in Beijing expressways,...A K-nearest neighbor （K-NN） based nonparametric regression model was proposed to predict travel speed for Beijing expressway. By using the historical traffic data collected from the detectors in Beijing expressways, a specically designed database was developed via the processes including data filtering, wavelet analysis and clustering. The relativity based weighted Euclidean distance was used as the distance metric to identify the K groups of nearest data series. Then, a K-NN nonparametric regression model was built to predict the average travel speeds up to 6 min into the future. Several randomly selected travel speed data series, collected from the floating car data （FCD） system, were used to validate the model. The results indicate that using the FCD, the model can predict average travel speeds with an accuracy of above 90%, and hence is feasible and effective.展开更多
The increasing popularity of e-commerce brings large volumes of sporadic orders from different customers,which have to be handled by freight trucks and distribution centers. To improve the level of service and reduce ...The increasing popularity of e-commerce brings large volumes of sporadic orders from different customers,which have to be handled by freight trucks and distribution centers. To improve the level of service and reduce the total shipping cost as well as traffic congestions in urban area, flexible methods and optimal vehicle routing strategies should be adopted to improve the efficiency of distribution effort. An optimization solution for vehicle routing and scheduling problem with time window for sporadic orders (VRPTW- S) was provided based on time-dependent travel time extracted from floating car data (FCD) with ArcGIS platform. A VRPTW-S model derived from the traditional vehicle routing problem was proposed, in which uncertainty of customer orders and travel time were considered. Based on this model, an advanced vehicle routing algorithm was designed to solve the problem. A case study of Shenzhen, Guangdong province, China, was conducted to demonstrate the vehicle operation flow,in which process of FCD and efficiency of delivery systems under different situations were discussed. The final results demonstrated a good performance of application of time-dependent travel time information using FCD in solving vehicle routing problems.展开更多
With the expansion of urban area and development of taxi system,problems arise,such as low operation efficiency,high taxi idling rate,and long passenger waiting-time. Although various studies have been conducted,only ...With the expansion of urban area and development of taxi system,problems arise,such as low operation efficiency,high taxi idling rate,and long passenger waiting-time. Although various studies have been conducted,only limited overview of the factors towards urban taxi system has been provided. Consequently,a comprehensive evaluation of taxi system is essential for the urban planner to analyze the current situation and take effective measures. This paper,by using Floating Car Data( FCD),proposes a Comprehensive Taxi Assessment Index( CTAI) to quantify the quality of existing urban taxi system with the assistance of Geographic Information System( GIS) technology. The proposed index system extracts and classifies key factors,reflecting the taxi system from the perspectives of operation efficiency,customer and taxi-driver satisfaction. The system contributes to improving the organization and operation of urban taxi system. Based on the data obtained from the city of Shenzhen,Guangdong Province,China,for both weekday and weekends( Dec.,2011),the proposed CTAI was illustrated by using the Principal Component Analysis( PCA) with ArcGIS 10. 0 platform. The results indicate that the system provides a good multi-dimensional view to delve into the existing urban taxi operation, thus to point out the most sensitive indices towards the entire system,which consequently provides guidelines for future improvement and management of urban taxi system.展开更多
After introducing the principle of float car data (FCD), this paper gives the primary flow of pre-handing and map- matching of the FCD. After analyzing the percentage of coverage of FCD on the road network, large quan...After introducing the principle of float car data (FCD), this paper gives the primary flow of pre-handing and map- matching of the FCD. After analyzing the percentage of coverage of FCD on the road network, large quantity of heritage database of routing status is used to estimate the routing velocity when lack of FCD on parts road segments. Multi liner regression model is then put forwarded by considering the spatial correlativity among the road network, and some model parameters are deduced when time series is classified in day and week. Besides, error of velocity probability and error of status probability are achieved based on the result from field testing while the feasibility and reliability of the velocity estimation model is obtained as well. Finally, as a case study in Shanghai center area, the whole routing velocity in the road network is estimated and published in real time.展开更多
Speed is of great importance to the safety level of a road. Speed choice is strongly influenced by the road environment and the drivers＇ assessment of safe speed level at a specific location. This paper presents an a...Speed is of great importance to the safety level of a road. Speed choice is strongly influenced by the road environment and the drivers＇ assessment of safe speed level at a specific location. This paper presents an analysis of the relationships between speed and road characteristics and speed and driver characteristics. The analysis is based on big data on speed and driver characteristics combined with data on road characteristics on 49 secondary rural two-lane roads in Denmark. Data is modelled using multivariate linear regression. The results show a primarily influence from road and shoulder width, the extent of road markings and the section lengths on speed. Secondly, they also show the presence of woodland and intersections influencing speed as gender, age of vehicle and time of day do.展开更多
为提高浮动车数据中异常数据检测能力及不同载客状态下的模型检测分析能力,提出基于S-DTA-IIForest(Summation&Difference Third Order Average&Improvement-Isolation Forest)的浮动车数据异常检测算法。构建由相邻两项求和(S...为提高浮动车数据中异常数据检测能力及不同载客状态下的模型检测分析能力,提出基于S-DTA-IIForest(Summation&Difference Third Order Average&Improvement-Isolation Forest)的浮动车数据异常检测算法。构建由相邻两项求和(S)、三阶求和平均差分(DTA)的二维度空间SDTA特征向量;提出差额累计更新和动态区分辨识的改进孤立森林IIForest算法,通过设置停止阈值参数,避免当出现新样本异常值分数大于停止阈值时,仅更新样本不更新孤立森林模型的问题,设计每个二叉树区分辨识度参数,区分辨识度位于停止区间时停止二叉树生长,提高算法收敛性能,以ROC(Receiver Operating Characteristic)曲线下面积AUC(Area Under ROC Cure)、F1-score为指标对模型精度进行对比分析,并以重庆市中心城区学府大道开展实例验证。结果表明:本文S-DTA-IIForest组合算法AUC、F1-score分别为86.63%、0.89,AUC较传统孤立森林IForest(Isolation Forest)提高32.4%,运行效率提高1.29%,具有收敛速度更快、精度更高的优势,载客条件下模型AUC、F1-score较未载客分别提高7.7%、10.8%,组合算法对载客数据有更高的检测精度,且未载客状态数据异常率较载客状态增加71.4%,未载客数据异常率更高。展开更多
针对在城市路网中大面积采集交通信息所存在的问题,提出了一种基于浮动车辆数据(floating car data,FCD)的城市道路车流速度估计算法,并通过FCD系统进行交通速度信息的采集.速度估计采用了一种改进的弧段Dijkstra路径寻优算法,在图的弧...针对在城市路网中大面积采集交通信息所存在的问题,提出了一种基于浮动车辆数据(floating car data,FCD)的城市道路车流速度估计算法,并通过FCD系统进行交通速度信息的采集.速度估计采用了一种改进的弧段Dijkstra路径寻优算法,在图的弧段-弧段存储结构中考虑了城市路网限制性道路交通信息的表达,并将路网的一些先验信息引入弧段关系结构中,提高了搜索效率和准确性.实验结果论证了所提出方法的有效性和可靠性.展开更多
Intelligent traffic system(ITS) is a development trend for urban modern traffic.Active guidance control for urban traffic can relieve increasing traffic congestion pressure effectively.FCD(floating car data) based dyn...Intelligent traffic system(ITS) is a development trend for urban modern traffic.Active guidance control for urban traffic can relieve increasing traffic congestion pressure effectively.FCD(floating car data) based dynamic guidance for urban traffic is one of the directions of traffic control research.To meet the real-time demand for massive FCD processing,an FCD parallel computing based dynamic traffic guidance approach is presented and implemented.The FCD properties are analyzed in detail.An FCD parallel computing based dynamic traffic guidance system is developed on KD-50-I-E platform.Experimental results demonstrate the effectiveness and feasibility of the proposed approach.展开更多
城市交通问题日趋严重,交通信息化服务成为了智能交通领域又一热点。基于浮动车(floating car data FCD)和DAB(digital audio broadcasting)的交通信息采集与服务系统,对交通信息数据源、数据处理及信息解码分发至终端等方面进行了研究...城市交通问题日趋严重,交通信息化服务成为了智能交通领域又一热点。基于浮动车(floating car data FCD)和DAB(digital audio broadcasting)的交通信息采集与服务系统,对交通信息数据源、数据处理及信息解码分发至终端等方面进行了研究,阐述了系统总体结构、关键技术、核心算法。该系统通过采集处理、多源数据信息融合、信息发布和信息终端软件开发,采用TPEG(transportprotocol experts group)信息编码技术,编码成二进制码流文件,并传输给DAB数字服务器进行信息分发,进而将交通信息实时传输到移动终端,为出行者提供可靠的、科学的交通信息服务。展开更多
浮动车数据(floating car data, FCD)技术是大规模城市路网交通流实时采集的有效方法.城市交通的动态诱导和控制需要对海量FCD进行快速处理.鉴于此,提出了FCD并行计算的动态任务调度方法.针对FCD数据包计算时间的不确定性和动态性,根据...浮动车数据(floating car data, FCD)技术是大规模城市路网交通流实时采集的有效方法.城市交通的动态诱导和控制需要对海量FCD进行快速处理.鉴于此,提出了FCD并行计算的动态任务调度方法.针对FCD数据包计算时间的不确定性和动态性,根据计算节点的处理能力进行数据包的动态分割,在处理过程中,采用动态任务分配策略以实现计算节点的同步.该方法在龙芯国产大数据一体机平台上进行了实现,并采用现场FCD数据进行了实验验证,结果表明,该方法较轮询和Min-Min调度算法,显著地提高了并行处理的性能.展开更多
It is a pressing task to estimate the real-time travel time on road networks reliably in big cities, even though floating car data has been widely used to reflect the real traffic. Currently floating car data are main...It is a pressing task to estimate the real-time travel time on road networks reliably in big cities, even though floating car data has been widely used to reflect the real traffic. Currently floating car data are mainly used to estimate the real-time traffic conditions on road segments, and has done little for turn delay estimation. However, turn delays on road intersections contribute significantly to the overall travel time on road networks in modem cities. In this paper, we present a technical framework to calculate the turn delays on road networks with float car data. First, the original floating car data collected with GPS equipped taxies was cleaned and matched to a street map with a distributed system based on Hadoop and MongoDB. Secondly, the refined trajectory data set was distributed among 96 time intervals （from 0：00 to 23： 59）. All of the intersections where the trajectories passed were connected with the trajectory segments, and constituted an experiment sample, while the intersections on arterial streets were specially selected to form another experiment sample. Thirdly, a principal curve-based algorithm was presented to estimate the turn delays at the given intersections. The algorithm argued is not only statistically fitted the real traffic conditions, but also is insensitive to data sparseness and missing data problems, which currently are almost inevitable with the widely used floating car data collecting technology. We adopted the floating car data collected from March to June in Beijing city in 2011, which contains more than 2.6 million trajectories generated from about 20000 GPS-equipped taxicabs and accounts for about 600 GB in data volume. The result shows the principal curve based algorithm we presented takes precedence over traditional methods, such as mean and median based approaches, and holds a higher estimation accuracy （about 10%-15% higher in RMSE）, as well as reflecting the changing trend of traffic congestion. With the estimation result for the travel delay at intersections, we analyzed the spatio-temporal distribution of turn delays in three time scenarios （0： 00-0： 15, 8： 15-8：30 and 12： 00-12： 15）. It indicates that during one＇s single trip in Beijing, average 60% of the travel time on the road networks is wasted on the intersections, and this situation is even worse in daytime. Although the 400 main intersections take only 2.7% of all the intersections, they occupy about 18% travel time.展开更多
Vehicles have been increasingly equipped with GPS receivers to record their trajectories,which we call floating car data.Compared with other data sources,these data are characterized by low cost,wide coverage,and rapi...Vehicles have been increasingly equipped with GPS receivers to record their trajectories,which we call floating car data.Compared with other data sources,these data are characterized by low cost,wide coverage,and rapid updating.The data have become an important source for road network extraction.In this paper,we propose a novel approach for mining road networks from floating car data.First,a Gaussian model is used to transform the data into bitmap,and the Otsu algorithm is utilized to detect road intersections.Then,a clothoid-based method is used to resample the GPS points to improve the clustering accuracy,and the data are clustered based on a distance-direction algorithm.Last,road centerlines are extracted with a weighted least squares algorithm.We report on experiments that were conducted on floating car data from Wuhan,China.To conclude,existing methods are compared with our method to prove that the proposed method is practical and effective.展开更多
As the travel purpose of non-occupied taxies is to find new passengers rather than to arrive at the destination, large differences exist in the route choice behavior between the occupied and non-occupied taxies.With t...As the travel purpose of non-occupied taxies is to find new passengers rather than to arrive at the destination, large differences exist in the route choice behavior between the occupied and non-occupied taxies.With the assistance of geographic information system(GIS) and taxi-based floating car data(FCD), this paper investigates the behavior differences between occupied and non-occupied taxi drivers with the same origin and destination. Descriptive statistical indexes from the FCD in Shenzhen, China are explored to identify the route choice characteristics of occupied and non-occupied taxies. Then, a conditional logit model is proposed to model the quantitative relationship between drivers' route choice and the related significant variables. Attributes of the variables related to non-occupied taxies' observed routes are compared with the case of occupied ones. The results indicate that, compared with their counterparts, non-occupied taxi drivers generally pay more attention to choosing arterial roads and avoiding congested segments. Additionally, they are also found less sensitive to fewer traffic lights and shorter travel time. Findings from this research can assist to improve urban road network planning and traffic management.展开更多
Public medical facilities that are closely related to the health of residents have been recognised as one of the most crucial elements in sustainable urban planning.For the sake of social equality of medical services(...Public medical facilities that are closely related to the health of residents have been recognised as one of the most crucial elements in sustainable urban planning.For the sake of social equality of medical services(especially for emergency medical conditions),the spatial distributions of medical resources need to be accurately measured and continuously optimized.This study presents an effective method to examine night emergency hospital visit and analyse its spatiotemporal characteristics using float car data(FCD).By extracting the hospital service areas,the two-step floating catchment area(2SFCA)methodology was improved to calculate hospital accessibility.Then,the balance between hospital accessibility and population density was analysed.In addition,we investigated the relationship between individual hospital choice preferences and hospital level and analysed several factors that affect individual choices.These results help us understand the special requirements and need of emergency hospital travel in cities and identify areas where medical resources are scarce.They can be used as guidance for urban hospital planning and construction.And the approach of hospital access behaviour investigation and the improved 2SFCA method can also provide insights for other activity-based travel behaviour research.展开更多
基金The Project of Research on Technologyand Devices for Traffic Guidance (Vehicle Navigation)System of Beijing Municipal Commission of Science and Technology(No H030630340320)the Project of Research on theIntelligence Traffic Information Platform of Beijing Education Committee
文摘A K-nearest neighbor （K-NN） based nonparametric regression model was proposed to predict travel speed for Beijing expressway. By using the historical traffic data collected from the detectors in Beijing expressways, a specically designed database was developed via the processes including data filtering, wavelet analysis and clustering. The relativity based weighted Euclidean distance was used as the distance metric to identify the K groups of nearest data series. Then, a K-NN nonparametric regression model was built to predict the average travel speeds up to 6 min into the future. Several randomly selected travel speed data series, collected from the floating car data （FCD） system, were used to validate the model. The results indicate that using the FCD, the model can predict average travel speeds with an accuracy of above 90%, and hence is feasible and effective.
基金National Natural Science Foundation of China(No.71101109)Shanghai Pujiang Program,China(No.12PJ1404600)
文摘The increasing popularity of e-commerce brings large volumes of sporadic orders from different customers,which have to be handled by freight trucks and distribution centers. To improve the level of service and reduce the total shipping cost as well as traffic congestions in urban area, flexible methods and optimal vehicle routing strategies should be adopted to improve the efficiency of distribution effort. An optimization solution for vehicle routing and scheduling problem with time window for sporadic orders (VRPTW- S) was provided based on time-dependent travel time extracted from floating car data (FCD) with ArcGIS platform. A VRPTW-S model derived from the traditional vehicle routing problem was proposed, in which uncertainty of customer orders and travel time were considered. Based on this model, an advanced vehicle routing algorithm was designed to solve the problem. A case study of Shenzhen, Guangdong province, China, was conducted to demonstrate the vehicle operation flow,in which process of FCD and efficiency of delivery systems under different situations were discussed. The final results demonstrated a good performance of application of time-dependent travel time information using FCD in solving vehicle routing problems.
基金Sponsored by the National Natural Science Foundation of China(Grant No.71101109)
文摘With the expansion of urban area and development of taxi system,problems arise,such as low operation efficiency,high taxi idling rate,and long passenger waiting-time. Although various studies have been conducted,only limited overview of the factors towards urban taxi system has been provided. Consequently,a comprehensive evaluation of taxi system is essential for the urban planner to analyze the current situation and take effective measures. This paper,by using Floating Car Data( FCD),proposes a Comprehensive Taxi Assessment Index( CTAI) to quantify the quality of existing urban taxi system with the assistance of Geographic Information System( GIS) technology. The proposed index system extracts and classifies key factors,reflecting the taxi system from the perspectives of operation efficiency,customer and taxi-driver satisfaction. The system contributes to improving the organization and operation of urban taxi system. Based on the data obtained from the city of Shenzhen,Guangdong Province,China,for both weekday and weekends( Dec.,2011),the proposed CTAI was illustrated by using the Principal Component Analysis( PCA) with ArcGIS 10. 0 platform. The results indicate that the system provides a good multi-dimensional view to delve into the existing urban taxi operation, thus to point out the most sensitive indices towards the entire system,which consequently provides guidelines for future improvement and management of urban taxi system.
文摘After introducing the principle of float car data (FCD), this paper gives the primary flow of pre-handing and map- matching of the FCD. After analyzing the percentage of coverage of FCD on the road network, large quantity of heritage database of routing status is used to estimate the routing velocity when lack of FCD on parts road segments. Multi liner regression model is then put forwarded by considering the spatial correlativity among the road network, and some model parameters are deduced when time series is classified in day and week. Besides, error of velocity probability and error of status probability are achieved based on the result from field testing while the feasibility and reliability of the velocity estimation model is obtained as well. Finally, as a case study in Shanghai center area, the whole routing velocity in the road network is estimated and published in real time.
文摘Speed is of great importance to the safety level of a road. Speed choice is strongly influenced by the road environment and the drivers＇ assessment of safe speed level at a specific location. This paper presents an analysis of the relationships between speed and road characteristics and speed and driver characteristics. The analysis is based on big data on speed and driver characteristics combined with data on road characteristics on 49 secondary rural two-lane roads in Denmark. Data is modelled using multivariate linear regression. The results show a primarily influence from road and shoulder width, the extent of road markings and the section lengths on speed. Secondly, they also show the presence of woodland and intersections influencing speed as gender, age of vehicle and time of day do.
文摘为提高浮动车数据中异常数据检测能力及不同载客状态下的模型检测分析能力,提出基于S-DTA-IIForest(Summation&Difference Third Order Average&Improvement-Isolation Forest)的浮动车数据异常检测算法。构建由相邻两项求和(S)、三阶求和平均差分(DTA)的二维度空间SDTA特征向量;提出差额累计更新和动态区分辨识的改进孤立森林IIForest算法,通过设置停止阈值参数,避免当出现新样本异常值分数大于停止阈值时,仅更新样本不更新孤立森林模型的问题,设计每个二叉树区分辨识度参数,区分辨识度位于停止区间时停止二叉树生长,提高算法收敛性能,以ROC(Receiver Operating Characteristic)曲线下面积AUC(Area Under ROC Cure)、F1-score为指标对模型精度进行对比分析,并以重庆市中心城区学府大道开展实例验证。结果表明:本文S-DTA-IIForest组合算法AUC、F1-score分别为86.63%、0.89,AUC较传统孤立森林IForest(Isolation Forest)提高32.4%,运行效率提高1.29%,具有收敛速度更快、精度更高的优势,载客条件下模型AUC、F1-score较未载客分别提高7.7%、10.8%,组合算法对载客数据有更高的检测精度,且未载客状态数据异常率较载客状态增加71.4%,未载客数据异常率更高。
文摘针对在城市路网中大面积采集交通信息所存在的问题,提出了一种基于浮动车辆数据(floating car data,FCD)的城市道路车流速度估计算法,并通过FCD系统进行交通速度信息的采集.速度估计采用了一种改进的弧段Dijkstra路径寻优算法,在图的弧段-弧段存储结构中考虑了城市路网限制性道路交通信息的表达,并将路网的一些先验信息引入弧段关系结构中,提高了搜索效率和准确性.实验结果论证了所提出方法的有效性和可靠性.
文摘Intelligent traffic system(ITS) is a development trend for urban modern traffic.Active guidance control for urban traffic can relieve increasing traffic congestion pressure effectively.FCD(floating car data) based dynamic guidance for urban traffic is one of the directions of traffic control research.To meet the real-time demand for massive FCD processing,an FCD parallel computing based dynamic traffic guidance approach is presented and implemented.The FCD properties are analyzed in detail.An FCD parallel computing based dynamic traffic guidance system is developed on KD-50-I-E platform.Experimental results demonstrate the effectiveness and feasibility of the proposed approach.
文摘城市交通问题日趋严重,交通信息化服务成为了智能交通领域又一热点。基于浮动车(floating car data FCD)和DAB(digital audio broadcasting)的交通信息采集与服务系统,对交通信息数据源、数据处理及信息解码分发至终端等方面进行了研究,阐述了系统总体结构、关键技术、核心算法。该系统通过采集处理、多源数据信息融合、信息发布和信息终端软件开发,采用TPEG(transportprotocol experts group)信息编码技术,编码成二进制码流文件,并传输给DAB数字服务器进行信息分发,进而将交通信息实时传输到移动终端,为出行者提供可靠的、科学的交通信息服务。
文摘浮动车数据(floating car data, FCD)技术是大规模城市路网交通流实时采集的有效方法.城市交通的动态诱导和控制需要对海量FCD进行快速处理.鉴于此,提出了FCD并行计算的动态任务调度方法.针对FCD数据包计算时间的不确定性和动态性,根据计算节点的处理能力进行数据包的动态分割,在处理过程中,采用动态任务分配策略以实现计算节点的同步.该方法在龙芯国产大数据一体机平台上进行了实现,并采用现场FCD数据进行了实验验证,结果表明,该方法较轮询和Min-Min调度算法,显著地提高了并行处理的性能.
基金This research was supported by the National Natural Science Foundation of China （Grant No. 41271408）, the National Hi-tech Research and Development Program of China （No. 2012AA12A211） and State Key Laboratory of Resources and Environmental Information System Open Foundation （No. 088RA500KA）. And we also thank the anonymous referees for their helpful comments and suggestions.
文摘It is a pressing task to estimate the real-time travel time on road networks reliably in big cities, even though floating car data has been widely used to reflect the real traffic. Currently floating car data are mainly used to estimate the real-time traffic conditions on road segments, and has done little for turn delay estimation. However, turn delays on road intersections contribute significantly to the overall travel time on road networks in modem cities. In this paper, we present a technical framework to calculate the turn delays on road networks with float car data. First, the original floating car data collected with GPS equipped taxies was cleaned and matched to a street map with a distributed system based on Hadoop and MongoDB. Secondly, the refined trajectory data set was distributed among 96 time intervals （from 0：00 to 23： 59）. All of the intersections where the trajectories passed were connected with the trajectory segments, and constituted an experiment sample, while the intersections on arterial streets were specially selected to form another experiment sample. Thirdly, a principal curve-based algorithm was presented to estimate the turn delays at the given intersections. The algorithm argued is not only statistically fitted the real traffic conditions, but also is insensitive to data sparseness and missing data problems, which currently are almost inevitable with the widely used floating car data collecting technology. We adopted the floating car data collected from March to June in Beijing city in 2011, which contains more than 2.6 million trajectories generated from about 20000 GPS-equipped taxicabs and accounts for about 600 GB in data volume. The result shows the principal curve based algorithm we presented takes precedence over traditional methods, such as mean and median based approaches, and holds a higher estimation accuracy （about 10%-15% higher in RMSE）, as well as reflecting the changing trend of traffic congestion. With the estimation result for the travel delay at intersections, we analyzed the spatio-temporal distribution of turn delays in three time scenarios （0： 00-0： 15, 8： 15-8：30 and 12： 00-12： 15）. It indicates that during one＇s single trip in Beijing, average 60% of the travel time on the road networks is wasted on the intersections, and this situation is even worse in daytime. Although the 400 main intersections take only 2.7% of all the intersections, they occupy about 18% travel time.
基金supported by the Joint Fund for Innovation and Development of Automobile Industry of National Natural Science Foundation of China[Grant Number U1764262]the National Natural Science Foundation of China[Grant Number 42101448].
文摘Vehicles have been increasingly equipped with GPS receivers to record their trajectories,which we call floating car data.Compared with other data sources,these data are characterized by low cost,wide coverage,and rapid updating.The data have become an important source for road network extraction.In this paper,we propose a novel approach for mining road networks from floating car data.First,a Gaussian model is used to transform the data into bitmap,and the Otsu algorithm is utilized to detect road intersections.Then,a clothoid-based method is used to resample the GPS points to improve the clustering accuracy,and the data are clustered based on a distance-direction algorithm.Last,road centerlines are extracted with a weighted least squares algorithm.We report on experiments that were conducted on floating car data from Wuhan,China.To conclude,existing methods are compared with our method to prove that the proposed method is practical and effective.
基金the Major Project of National Social Science Foundation of China(No.16ZDA048)the Shanghai Municipal Natural Science Foundation,China(No.17ZR1445500)the Humanities and Social Science Research Project of Ministry of Education,China(No.15YJCZH148)
文摘As the travel purpose of non-occupied taxies is to find new passengers rather than to arrive at the destination, large differences exist in the route choice behavior between the occupied and non-occupied taxies.With the assistance of geographic information system(GIS) and taxi-based floating car data(FCD), this paper investigates the behavior differences between occupied and non-occupied taxi drivers with the same origin and destination. Descriptive statistical indexes from the FCD in Shenzhen, China are explored to identify the route choice characteristics of occupied and non-occupied taxies. Then, a conditional logit model is proposed to model the quantitative relationship between drivers' route choice and the related significant variables. Attributes of the variables related to non-occupied taxies' observed routes are compared with the case of occupied ones. The results indicate that, compared with their counterparts, non-occupied taxi drivers generally pay more attention to choosing arterial roads and avoiding congested segments. Additionally, they are also found less sensitive to fewer traffic lights and shorter travel time. Findings from this research can assist to improve urban road network planning and traffic management.
基金supported by National Natural Science Foundation of China[grant no 42171452].
文摘Public medical facilities that are closely related to the health of residents have been recognised as one of the most crucial elements in sustainable urban planning.For the sake of social equality of medical services(especially for emergency medical conditions),the spatial distributions of medical resources need to be accurately measured and continuously optimized.This study presents an effective method to examine night emergency hospital visit and analyse its spatiotemporal characteristics using float car data(FCD).By extracting the hospital service areas,the two-step floating catchment area(2SFCA)methodology was improved to calculate hospital accessibility.Then,the balance between hospital accessibility and population density was analysed.In addition,we investigated the relationship between individual hospital choice preferences and hospital level and analysed several factors that affect individual choices.These results help us understand the special requirements and need of emergency hospital travel in cities and identify areas where medical resources are scarce.They can be used as guidance for urban hospital planning and construction.And the approach of hospital access behaviour investigation and the improved 2SFCA method can also provide insights for other activity-based travel behaviour research.
