RFID交通数据时间覆盖率分析

在交通状态判别领域,针对磁感应线圈的"时间占有率"参数得到广泛应用.由于RFID交通信息采集技术无法准确获得车辆占据检测区域内的时长,因此,基于对RFID数据特性的分析,提出时间覆盖率的概念及计算方法.选取7种时间汇集度进行时间覆盖率的计算,根据计算结果画出基站的时间覆盖率随时间汇集度变化的折线图,由折线图走势可对基站的工作状态、基站所在道路的流量大小及交通流的连续性做出初步判断.选取南京市区主干道上21个RFID基站的原始数据,对所提出的方法进行实例分析,发现基站的时间覆盖率折线图可分为3种类型:①日覆盖率小于100%;②日覆盖率等于100%,并且小时覆盖率至5 min覆盖率接近于100%;③日覆盖率等于100%,并且小时覆盖率至5 min覆盖率中出现了下降.每种类型的折线图对应一定的基站工作状态和道路交通流特性.由分析结果可看出,时间覆盖率这一指标对RFID基站自身性能评判和交通流状态分析都具有一定的实际意义. 

An Analysis on Time Coverage Rate of RFID Traffic Data

In the field of road traffic status identification, parameters on "time occupancy" based on data collected from magnetic loops have been widely used.However, such data cannot be obtained from traffic flow data collection methods based RFID technologies.Based on the analyses of RFID data characteristics, this paper proposes a novel concept of Time Coverage Rate (TCR) and its calculation method.TCRs are calculated with the consideration of 7 types of time aggregation levels.Curves of base stations' TCRs taking time aggregation levels as an independent variable are drawn according to the calculation results.Status of the base stations, the volume as well as the continuity of the traffic flow at the base stations' location can be roughly estimated based on the trends of these curves.21 RFID base stations on arterials of Nanjing are chosen for a case study in which the proposed approach is used.The results show that the curves of the TCRs can be categorized into 3 types, including: ① Daily coverage rate is less than 100%.② Daily coverage rate is equal to 100% and time aggregation is between 1 h and 5 min, TCRs are near to 100%;③ Daily coverage rate is equal to 100% and time aggregation is between 1 h and 5 min, TCRs decrease.Each type represents a certain working condition of base stations and different characteristics of traffic flow.It can be seen that, time coverage rate has practical significance for performance evaluation of RFID base stations and analyses of traffic flow statuses.