線性轉換函數(Transfer Function) ，通常可用來描述具有時間序列之單變量(Uni variate) 或雙變量(Bi var i ate) 之關係。例如:以固定式偵測器獲取交通資料之動態系統( Dynam i c System) 下之成對觀察變量(Xt， Yt) 為得自等時距之相關變量，其中X 變量可視為密度(Density) 輸入(Input) ，而Y變量為速率(Speed) 輸出，此法之優點在於其非特定性，理論上應可適用於各種動態系統，但其缺點為已知運用本方法之實例相當少。
本研究以模擬分析(PARAMICS) 為基礎，結合資訊轉換模式將固定偵測器之點資料轉換為路段平均密度，以及速率與密度關，進而探討轉換函數模式在預測旅行時間之運用。據此本研究之主要內容包括(1)以模擬固定式偵測器佈設為基礎下， 搭配轉換函數模式進行旅行時間之推算; (2) 以轉換函數模式搭配滾動平面法進行離線操作(Off-line)旅行時間預測。
本研究之完整演算法分兩階段進行，第一階段為路段平均密度時間演算法，係利用上、下游兩偵測器在即時提供之點資訊中推算路段平均密度，並依此推估路段旅行時間。第二階段為轉換函數模式，當速率與密度兩變數皆已知時，即可探討兩者間的動態(依時性)轉換關餘，進而推估旅行時間。
本研究選取國道一號北部路段為模擬實際路網，成功地探討與整合轉換函數模式與路段平均密度時間演算法在預測旅行時間之運用，並依此示範了此混合演算之流程與程序，整合轉換模式模式推估路段平均密度。此外， 本研究並進一步探討偵測器基礎佈設策略與增設佈設策略兩種偵測器佈設情境，驗證分析單純路段密度模式與混合轉換函數模式之演算效果。其結果顯示，在基礎佈設策略下，動態轉換函數在旅行時間推估上是有顯著改善單純路段密度模式; 在增設佈設策下模式校估結果卻不符合預期假設，此亦顯示以上、下游兩組偵測器所定義之路段長度愈短交通資訊隨時間變化之變異愈大，進而影響預測模式之穩定性與準確度。 Dual-loop vehicle detectors are most commonly used devices in this country to perform instantaneous (real time) traffic data collection for either traffic management or travel information. ln particular, travel time information is of the major importance which can not be obtained directly but derived from various models/algorithms using detected traffic flow related data as input.
Among many travel time estimation models/algorithms, traffic flow based algorithms are particular attractive due to their robustness in accordance to theory rather than some ""black boxes"" approaches. ln addition, transfer function methods with the capability to calibrate speed-density relations using time series data was recognized to capture the effect of dynamic nature real time data instead of the commonly used static. It is therefore the focus of this study to develop an integrated procedure of the two in the application of estimation of travel time along a specific road segment. One particular algorithm of interested was the recently derived by Oh,Jayakrishnan and Recker in 2002 with the concept of section density seems appealing due to its simplicity and theoretical
clearness in presentation. This study accessed Paramics, a microscopic traffic simulation program, as primary research tool of data sources to evaluate the proposed issues. It is because the vehicle detection system is under major overhaul for some sustained period hence reliable and continuous true data would not be available in the study area. The Paramics was carefully calibrated utilizing its feature for detailed road section geometric configuration and driving behavior the selected freeway section.
The estimation results using the proposed integrated method (with transfer function) were evaluated in contrast to a base model with steady-state speed-density)relation under two VD (vehicle detector) deployment scenarios, one with original deployment and another with incremental deployment. The results show that the hybrid model did not always perform better than the base model in all cases especially under the incremental deployment scenario. The reason may be identified to the poor synergy of the nature of the section density model using the deviation of flow rates and the relatively high fluctuation of simulated flow pattern short freeway sections within relative short and varying time interval by Paramics.
關聯:
中華民國運輸學會第二十屆學術論文研討會論文集 (第三冊)=Proceeding of the 20th annual conference for the Chinese institute of transportation v.3，頁907-926
