外文翻譯--車輛檢測技術(shù)在交通管理上的應(yīng)用-交通線路-展示頁
2025-05-27 05:49本頁面
【正文】 ware. This increases the installation cost or the real purchase price of the detector. Furthermore, not every detector outputs data on an individual vehicle basis. While some do, others integrate the data and output the results over periods that range from tens of seconds to minutes, producing parameters that are characteristic of macroscopic traffic flow. The traffic management agency must thus use caution when paring outputs from dissimilar detectors. In performing the technology evaluations and in analyzing the data, focus was placed on the underlying technology upon which the detectors were based [1,2]. It was not the purpose of the program to determine which specific detectors met a set of requirements, but rather whether the sensing technology they used had merit in measuring and reporting traffic data to the accuracy needed for present a nd future applications. Obviously, there can be many implementations of a technology, some of which may be better exploited than others at any time. Thus, a technology may show promise for future applications, but the stateoftheart of current hardware or software may be hampering its present deployment. The detectors that were used in the technology evaluations during the field tests are listed in Table 1. Not all detectors were available at all sites as shown in the footnotes to the table. A summary of the advantages and disadvantages of the detector technologies is given in Table 2. Some of them are application specific, implying that a particular technology may be suitable for some but not all applications. A factor not addressed in this table is detector cost. This issue is again application specific. For example, a higher cost detector may be appropriate for an application requiring specific data or multiple detection zones (suitable for multiple lane coverage) that are incorporated into the more expensive detector. Table 3 shows examples of overhead detector technology patibility with several traffic management applications. The assumptions shown concerning the application dictate, in part, the appropriateness of the technology. THEORY OF OVERHEAD DETECTOR OPERATION The following paragraphs give a brief explanation of the underlying operating principles for microwave, passive infrared, active infrared, ultrasonic, passive acoustic, and video image processor detectors. Microwave Radar Microwave radars used in the . for vehicle detection transmit energy at GHz, a frequency allocated by the FCC for this purpose. Their output power is regulated by the FCC and certified by the manufacturer to meet FCC requirements. No further certification is required of the transportation agencies for their deployment. Two types of microwave radar detectors are used in traffic management applications. The first transmits electromagic energy at a constant frequency. It measures the speed of vehicles within its field of view using the Doppler principle, where the difference in frequency between the transmitted and received signals is proportional to the vehicle speed. Thus, the detection of a frequency shift denotes the passage of a vehicle. This type of detector cannot detect stopped vehicles and is, therefore, not suitable for applications that require vehicle presence such as at a signal light or
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