減少通訊需求之交通通報系統

Abstract

提供用路人即時交通資訊，包含車速、車流量等資訊，可節省行車時間及能源消耗。由於GPS與無線資料傳輸逐漸普及，利用GPS探偵車回報車速取得即時交通資訊成為可行的方式。相對於傳統固定式車輛偵測器而言，GPS探偵車大幅降低佈建與維護成本。然而目前GPS探偵車定期回報車速到交通資訊中心彙整。要取得即時路況，必須採用較短的回報週期，如此可能造成回報資訊超載的問題。本研究提出雙向回報方式，改良探偵車交通資訊回報機制，能有效降低交通資訊回報次數和成本。由交通資訊中心透過無線網路週期性地廣播各路段之即時最高車速，並由車速較快之探偵車先回傳即時車速至交通資訊中心，再由交通資訊中心廣播回報最快車速。其他車速較慢之探偵車則不再回報車速。此一方法也適用於取得各路段的最短行車時間。為了分析系統效能，我們使用運輸模擬軟體VISSIM來進行實驗模擬。研究成果證實，我們所提出的方法可減少探偵車資訊回報之數量，減輕交通資訊中心之負載。研究結果也表明利用最高速度以及最短行車時間來顯示交通狀況是可行的。

Providing real-time traffic information, such as traffic speed and flow, to road users can save traveling time and reduce fuel consumption. With the increasing popularity of on-board GPS devices and wireless data communication capability, it becomes feasible to obtain global real-time traffic information from GPS-equipped probe cars, which periodically report speed to a traffic information center (TIC). To provide real-time information, the report period needs to be short. This may result in a huge number of reports to an over-loaded TIC. In this thesis, we present a traffic report system and method with fast feedback to reduce the number of traffic reports from probe cars. The TIC periodically broadcasts the maximum speed collected in the previous period for each road segment. After receiving the TIC broadcast, probe cars with fast speed would report their speed to the TIC earlier than those with slow speed. The TIC will also broadcast the maximum speed of this cycle immediately after it receives a speed report. This immediate broadcast would prevent slow-moving probe cars from reporting their speeds. The same method can be used to obtain the minimum travel time as well. To evaluate the performance of the system, we have performed simulations using the traffic model simulator VISSIM. The simulation results indicate that our approach significantly reduces the number of traffic reports and the loading of the TIC. The results also suggest that it is feasible to use the maximum speed and the minimum travel time to indicate traffic conditions.